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 $118.75   12.104%   $133.1235   $133.12   $133.10   $133.10  
  Purchase #2 $57.82   9.618%   $63.3811   $63.38   $63.40   $63.40  
  Purchase #3 $187.94   3.114%   $193.7925   $193.79   $193.80   $193.80  
  Purchase #4 $85.89   11.179%   $95.4916   $95.49   $95.50   $95.50  
  Purchase #5 $55.39   8.628%   $60.169   $60.17   $60.15   $60.20  
  Purchase #6 $96.98   11.502%   $108.1346   $108.13   $108.15   $108.10  
  Purchase #7 $127.38   3.769%   $132.181   $132.18   $132.20   $132.20  
  7 purchase totals = $730.15       $786.2733   $786.26   $786.30   $786.30