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 $234.71   12.161%   $263.2531   $263.25   $263.25   $263.30  
  Purchase #2 $209.65   5.652%   $221.4994   $221.50   $221.50   $221.50  
  Purchase #3 $88.47   5.288%   $93.1483   $93.15   $93.15   $93.10  
  Purchase #4 $89.26   8.805%   $97.1193   $97.12   $97.10   $97.10  
  Purchase #5 $121.27   3.405%   $125.3992   $125.40   $125.40   $125.40  
  Purchase #6 $11.54   3.265%   $11.9168   $11.92   $11.90   $11.90  
  Purchase #7 $149.75   10.143%   $164.9391   $164.94   $164.95   $164.90  
  7 purchase totals = $904.65       $977.2752   $977.28   $977.25   $977.20