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 $45.64   5.185%   $48.0064   $48.01   $48.00   $48.00  
  Purchase #2 $88.61   7.767%   $95.4923   $95.49   $95.50   $95.50  
  Purchase #3 $182.79   8.138%   $197.6655   $197.67   $197.65   $197.70  
  Purchase #4 $204.34   12.515%   $229.9132   $229.91   $229.90   $229.90  
  Purchase #5 $132.90   12.535%   $149.559   $149.56   $149.55   $149.60  
  Purchase #6 $54.51   4.713%   $57.0791   $57.08   $57.10   $57.10  
  Purchase #7 $170.35   5.505%   $179.7278   $179.73   $179.75   $179.70  
  7 purchase totals = $879.14       $957.4433   $957.45   $957.45   $957.50