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 $58.71   10.428%   $64.8323   $64.83   $64.85   $64.80  
  Purchase #2 $199.25   4.225%   $207.6683   $207.67   $207.65   $207.70  
  Purchase #3 $16.64   4.604%   $17.4061   $17.41   $17.40   $17.40  
  Purchase #4 $162.49   11.341%   $180.918   $180.92   $180.90   $180.90  
  Purchase #5 $233.62   11.409%   $260.2737   $260.27   $260.25   $260.30  
  Purchase #6 $186.69   5.545%   $197.042   $197.04   $197.05   $197.00  
  Purchase #7 $74.86   11.167%   $83.2196   $83.22   $83.20   $83.20  
  7 purchase totals = $932.26       $1,011.3600   $1,011.36   $1,011.30   $1,011.30