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 $107.41   10.766%   $118.9738   $118.97   $118.95   $119.00  
  Purchase #2 $84.54   10.300%   $93.2476   $93.25   $93.25   $93.20  
  Purchase #3 $72.38   4.861%   $75.8984   $75.90   $75.90   $75.90  
  Purchase #4 $247.79   6.742%   $264.496   $264.50   $264.50   $264.50  
  Purchase #5 $34.35   10.269%   $37.8774   $37.88   $37.90   $37.90  
  Purchase #6 $229.27   13.809%   $260.9299   $260.93   $260.95   $260.90  
  Purchase #7 $129.90   9.354%   $142.0508   $142.05   $142.05   $142.10  
  7 purchase totals = $905.64       $993.4739   $993.48   $993.50   $993.50