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 $47.59   11.822%   $53.2161   $53.22   $53.20   $53.20  
  Purchase #2 $60.30   8.132%   $65.2036   $65.20   $65.20   $65.20  
  Purchase #3 $235.77   5.706%   $249.223   $249.22   $249.20   $249.20  
  Purchase #4 $141.47   11.455%   $157.6754   $157.68   $157.70   $157.70  
  Purchase #5 $148.70   4.739%   $155.7469   $155.75   $155.75   $155.70  
  Purchase #6 $125.63   12.492%   $141.3237   $141.32   $141.30   $141.30  
  Purchase #7 $220.27   7.536%   $236.8695   $236.87   $236.85   $236.90  
  7 purchase totals = $979.73       $1,059.2582   $1,059.26   $1,059.20   $1,059.20