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 $52.92   11.475%   $58.9926   $58.99   $59.00   $59.00  
  Purchase #2 $55.58   13.299%   $62.9716   $62.97   $62.95   $63.00  
  Purchase #3 $122.57   12.682%   $138.1143   $138.11   $138.10   $138.10  
  Purchase #4 $132.25   6.874%   $141.3409   $141.34   $141.35   $141.30  
  Purchase #5 $204.77   7.610%   $220.353   $220.35   $220.35   $220.40  
  Purchase #6 $187.46   8.389%   $203.186   $203.19   $203.20   $203.20  
  Purchase #7 $125.73   9.685%   $137.907   $137.91   $137.90   $137.90  
  7 purchase totals = $881.28       $962.8654   $962.86   $962.85   $962.90