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 $30.66   10.722%   $33.9474   $33.95   $33.95   $33.90  
  Purchase #2 $141.82   10.388%   $156.5523   $156.55   $156.55   $156.60  
  Purchase #3 $223.89   9.197%   $244.4812   $244.48   $244.50   $244.50  
  Purchase #4 $37.90   7.546%   $40.7599   $40.76   $40.75   $40.80  
  Purchase #5 $191.86   8.339%   $207.8592   $207.86   $207.85   $207.90  
  Purchase #6 $140.25   4.246%   $146.205   $146.21   $146.20   $146.20  
  Purchase #7 $175.91   10.380%   $194.1695   $194.17   $194.15   $194.20  
  7 purchase totals = $942.29       $1,023.9745   $1,023.98   $1,023.95   $1,024.10