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 $64.94   5.221%   $68.3305   $68.33   $68.35   $68.30  
  Purchase #2 $238.61   7.404%   $256.2767   $256.28   $256.30   $256.30  
  Purchase #3 $45.81   4.604%   $47.9191   $47.92   $47.90   $47.90  
  Purchase #4 $157.43   10.427%   $173.8452   $173.85   $173.85   $173.80  
  Purchase #5 $146.63   10.390%   $161.8649   $161.86   $161.85   $161.90  
  Purchase #6 $111.92   5.719%   $118.3207   $118.32   $118.30   $118.30  
  Purchase #7 $118.80   6.606%   $126.6479   $126.65   $126.65   $126.60  
  7 purchase totals = $884.14       $953.2050   $953.21   $953.20   $953.10