Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $91.56   13.297%   $103.7347   $103.73   $103.75   $103.70  
  Purchase #2 $181.96   12.382%   $204.4903   $204.49   $204.50   $204.50  
  Purchase #3 $159.69   12.488%   $179.6321   $179.63   $179.65   $179.60  
  Purchase #4 $32.47   7.723%   $34.9777   $34.98   $35.00   $35.00  
  Purchase #5 $97.63   11.368%   $108.7286   $108.73   $108.75   $108.70  
  Purchase #6 $110.97   8.719%   $120.6455   $120.65   $120.65   $120.60  
  Purchase #7 $170.72   6.824%   $182.3699   $182.37   $182.35   $182.40  
  7 purchase totals = $845.00       $934.5788   $934.58   $934.65   $934.50