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 $34.89   8.718%   $37.9317   $37.93   $37.95   $37.90  
  Purchase #2 $125.83   12.285%   $141.2882   $141.29   $141.30   $141.30  
  Purchase #3 $107.64   4.750%   $112.7529   $112.75   $112.75   $112.80  
  Purchase #4 $161.55   3.162%   $166.6582   $166.66   $166.65   $166.70  
  Purchase #5 $154.82   3.296%   $159.9229   $159.92   $159.90   $159.90  
  Purchase #6 $62.27   6.231%   $66.15   $66.15   $66.15   $66.20  
  Purchase #7 $13.68   10.747%   $15.1502   $15.15   $15.15   $15.20  
  7 purchase totals = $660.68       $699.8541   $699.85   $699.85   $700.00