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 $39.46   4.468%   $41.2231   $41.22   $41.20   $41.20  
  Purchase #2 $60.44   10.663%   $66.8847   $66.88   $66.90   $66.90  
  Purchase #3 $188.79   13.864%   $214.9638   $214.96   $214.95   $215.00  
  Purchase #4 $226.27   7.177%   $242.5094   $242.51   $242.50   $242.50  
  Purchase #5 $33.32   7.326%   $35.761   $35.76   $35.75   $35.80  
  Purchase #6 $210.67   6.336%   $224.0181   $224.02   $224.00   $224.00  
  Purchase #7 $132.66   13.794%   $150.9591   $150.96   $150.95   $151.00  
  7 purchase totals = $891.61       $976.3192   $976.31   $976.25   $976.40