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 $14.39   13.484%   $16.3303   $16.33   $16.35   $16.30  
  Purchase #2 $45.91   5.853%   $48.5971   $48.60   $48.60   $48.60  
  Purchase #3 $82.59   11.595%   $92.1663   $92.17   $92.15   $92.20  
  Purchase #4 $83.98   9.701%   $92.1269   $92.13   $92.15   $92.10  
  Purchase #5 $56.26   6.799%   $60.0851   $60.09   $60.10   $60.10  
  Purchase #6 $239.34   11.546%   $266.9742   $266.97   $266.95   $267.00  
  Purchase #7 $33.33   7.441%   $35.8101   $35.81   $35.80   $35.80  
  7 purchase totals = $555.80       $612.0900   $612.10   $612.10   $612.10