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 $49.32   7.372%   $52.9559   $52.96   $52.95   $53.00  
  Purchase #2 $229.80   3.275%   $237.326   $237.33   $237.35   $237.30  
  Purchase #3 $143.95   10.439%   $158.9769   $158.98   $159.00   $159.00  
  Purchase #4 $136.66   4.121%   $142.2918   $142.29   $142.30   $142.30  
  Purchase #5 $87.48   9.590%   $95.8693   $95.87   $95.85   $95.90  
  Purchase #6 $113.38   10.847%   $125.6783   $125.68   $125.70   $125.70  
  Purchase #7 $122.96   12.874%   $138.7899   $138.79   $138.80   $138.80  
  7 purchase totals = $883.55       $951.8881   $951.90   $951.95   $952.00