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 $55.74   11.176%   $61.9695   $61.97   $61.95   $62.00  
  Purchase #2 $48.53   8.647%   $52.7264   $52.73   $52.75   $52.70  
  Purchase #3 $224.74   8.857%   $244.6452   $244.65   $244.65   $244.60  
  Purchase #4 $209.90   10.205%   $231.3203   $231.32   $231.30   $231.30  
  Purchase #5 $209.71   9.790%   $230.2406   $230.24   $230.25   $230.20  
  Purchase #6 $8.70   11.309%   $9.6839   $9.68   $9.70   $9.70  
  Purchase #7 $37.69   7.390%   $40.4753   $40.48   $40.50   $40.50  
  7 purchase totals = $795.01       $871.0612   $871.07   $871.10   $871.00