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 $94.33   4.435%   $98.5135   $98.51   $98.50   $98.50  
  Purchase #2 $135.70   5.469%   $143.1214   $143.12   $143.10   $143.10  
  Purchase #3 $66.51   12.866%   $75.0672   $75.07   $75.05   $75.10  
  Purchase #4 $26.91   3.855%   $27.9474   $27.95   $27.95   $27.90  
  Purchase #5 $185.45   13.496%   $210.4783   $210.48   $210.50   $210.50  
  Purchase #6 $162.96   13.532%   $185.0117   $185.01   $185.00   $185.00  
  Purchase #7 $180.95   8.242%   $195.8639   $195.86   $195.85   $195.90  
  7 purchase totals = $852.81       $936.0034   $936.00   $935.95   $936.00