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 $239.43   6.199%   $254.2723   $254.27   $254.25   $254.30  
  Purchase #2 $214.43   10.444%   $236.8251   $236.83   $236.85   $236.80  
  Purchase #3 $118.97   6.341%   $126.5139   $126.51   $126.50   $126.50  
  Purchase #4 $211.32   6.175%   $224.369   $224.37   $224.35   $224.40  
  Purchase #5 $19.96   3.328%   $20.6243   $20.62   $20.60   $20.60  
  Purchase #6 $46.70   3.452%   $48.3121   $48.31   $48.30   $48.30  
  Purchase #7 $13.72   5.469%   $14.4703   $14.47   $14.45   $14.50  
  7 purchase totals = $864.53       $925.3870   $925.38   $925.30   $925.40