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 $57.56   11.770%   $64.3348   $64.33   $64.35   $64.30  
  Purchase #2 $60.83   5.670%   $64.2791   $64.28   $64.30   $64.30  
  Purchase #3 $38.44   11.826%   $42.9859   $42.99   $43.00   $43.00  
  Purchase #4 $216.61   4.749%   $226.8968   $226.90   $226.90   $226.90  
  Purchase #5 $97.46   3.663%   $101.03   $101.03   $101.05   $101.00  
  Purchase #6 $183.78   13.760%   $209.0681   $209.07   $209.05   $209.10  
  Purchase #7 $119.85   4.854%   $125.6675   $125.67   $125.65   $125.70  
  7 purchase totals = $774.53       $834.2622   $834.27   $834.30   $834.30