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 $236.32   12.541%   $265.9569   $265.96   $265.95   $266.00  
  Purchase #2 $196.43   5.733%   $207.6913   $207.69   $207.70   $207.70  
  Purchase #3 $41.65   8.361%   $45.1324   $45.13   $45.15   $45.10  
  Purchase #4 $229.95   7.830%   $247.9551   $247.96   $247.95   $248.00  
  Purchase #5 $69.56   3.483%   $71.9828   $71.98   $72.00   $72.00  
  Purchase #6 $27.72   3.237%   $28.6173   $28.62   $28.60   $28.60  
  Purchase #7 $97.30   6.502%   $103.6264   $103.63   $103.65   $103.60  
  7 purchase totals = $898.93       $970.9622   $970.97   $971.00   $971.00