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 $84.72   9.328%   $92.6227   $92.62   $92.60   $92.60  
  Purchase #2 $23.36   11.138%   $25.9618   $25.96   $25.95   $26.00  
  Purchase #3 $129.41   11.838%   $144.7296   $144.73   $144.75   $144.70  
  Purchase #4 $65.60   4.182%   $68.3434   $68.34   $68.35   $68.30  
  Purchase #5 $146.66   11.232%   $163.1329   $163.13   $163.15   $163.10  
  Purchase #6 $226.69   13.696%   $257.7375   $257.74   $257.75   $257.70  
  Purchase #7 $53.51   13.709%   $60.8457   $60.85   $60.85   $60.80  
  7 purchase totals = $729.95       $813.3736   $813.37   $813.40   $813.20