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 $42.50   10.546%   $46.9821   $46.98   $47.00   $47.00  
  Purchase #2 $71.44   5.761%   $75.5557   $75.56   $75.55   $75.60  
  Purchase #3 $39.51   13.299%   $44.7644   $44.76   $44.75   $44.80  
  Purchase #4 $21.99   5.126%   $23.1172   $23.12   $23.10   $23.10  
  Purchase #5 $173.43   5.689%   $183.2964   $183.30   $183.30   $183.30  
  Purchase #6 $45.29   7.433%   $48.6564   $48.66   $48.65   $48.70  
  Purchase #7 $200.41   8.592%   $217.6292   $217.63   $217.65   $217.60  
  7 purchase totals = $594.57       $640.0014   $640.01   $640.00   $640.10