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 $59.80   5.287%   $62.9616   $62.96   $62.95   $63.00  
  Purchase #2 $12.67   13.299%   $14.355   $14.36   $14.35   $14.40  
  Purchase #3 $141.45   7.421%   $151.947   $151.95   $151.95   $151.90  
  Purchase #4 $244.77   5.182%   $257.454   $257.45   $257.45   $257.50  
  Purchase #5 $171.69   8.189%   $185.7497   $185.75   $185.75   $185.70  
  Purchase #6 $83.28   11.184%   $92.594   $92.59   $92.60   $92.60  
  Purchase #7 $209.57   13.660%   $238.1973   $238.20   $238.20   $238.20  
  7 purchase totals = $923.23       $1,003.2586   $1,003.26   $1,003.25   $1,003.30