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 $84.82   9.347%   $92.7481   $92.75   $92.75   $92.70  
  Purchase #2 $245.54   10.854%   $272.1909   $272.19   $272.20   $272.20  
  Purchase #3 $237.53   8.351%   $257.3661   $257.37   $257.35   $257.40  
  Purchase #4 $59.99   10.250%   $66.139   $66.14   $66.15   $66.10  
  Purchase #5 $47.88   11.646%   $53.4561   $53.46   $53.45   $53.50  
  Purchase #6 $157.72   8.350%   $170.8896   $170.89   $170.90   $170.90  
  Purchase #7 $50.33   3.597%   $52.1404   $52.14   $52.15   $52.10  
  7 purchase totals = $883.81       $964.9302   $964.94   $964.95   $964.90