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 $52.37   9.280%   $57.2299   $57.23   $57.25   $57.20  
  Purchase #2 $46.97   13.528%   $53.3241   $53.32   $53.30   $53.30  
  Purchase #3 $188.85   10.787%   $209.2212   $209.22   $209.20   $209.20  
  Purchase #4 $97.48   8.439%   $105.7063   $105.71   $105.70   $105.70  
  Purchase #5 $240.77   11.628%   $268.7667   $268.77   $268.75   $268.80  
  Purchase #6 $53.75   6.423%   $57.2024   $57.20   $57.20   $57.20  
  Purchase #7 $110.75   9.560%   $121.3377   $121.34   $121.35   $121.30  
  7 purchase totals = $790.94       $872.7883   $872.79   $872.75   $872.70