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 $48.97   8.202%   $52.9865   $52.99   $53.00   $53.00  
  Purchase #2 $226.85   12.451%   $255.0951   $255.10   $255.10   $255.10  
  Purchase #3 $200.26   8.667%   $217.6165   $217.62   $217.60   $217.60  
  Purchase #4 $26.31   10.713%   $29.1286   $29.13   $29.15   $29.10  
  Purchase #5 $139.86   9.202%   $152.7299   $152.73   $152.75   $152.70  
  Purchase #6 $54.69   5.331%   $57.6055   $57.61   $57.60   $57.60  
  Purchase #7 $149.72   5.544%   $158.0205   $158.02   $158.00   $158.00  
  7 purchase totals = $846.66       $923.1826   $923.20   $923.20   $923.10