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 $61.55   7.544%   $66.1933   $66.19   $66.20   $66.20  
  Purchase #2 $59.73   4.397%   $62.3563   $62.36   $62.35   $62.40  
  Purchase #3 $138.32   3.291%   $142.8721   $142.87   $142.85   $142.90  
  Purchase #4 $144.38   5.384%   $152.1534   $152.15   $152.15   $152.20  
  Purchase #5 $13.96   7.761%   $15.0434   $15.04   $15.05   $15.00  
  Purchase #6 $210.47   7.818%   $226.9245   $226.92   $226.90   $226.90  
  Purchase #7 $187.54   5.751%   $198.3254   $198.33   $198.35   $198.30  
  7 purchase totals = $815.95       $863.8684   $863.86   $863.85   $863.90