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 $111.27   5.718%   $117.6324   $117.63   $117.65   $117.60  
  Purchase #2 $53.77   13.797%   $61.1886   $61.19   $61.20   $61.20  
  Purchase #3 $250.46   3.871%   $260.1553   $260.16   $260.15   $260.20  
  Purchase #4 $55.43   5.236%   $58.3323   $58.33   $58.35   $58.30  
  Purchase #5 $99.92   4.113%   $104.0297   $104.03   $104.05   $104.00  
  Purchase #6 $101.78   12.511%   $114.5137   $114.51   $114.50   $114.50  
  Purchase #7 $44.72   10.421%   $49.3803   $49.38   $49.40   $49.40  
  7 purchase totals = $717.35       $765.2323   $765.23   $765.30   $765.20