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 $55.98   10.146%   $61.6597   $61.66   $61.65   $61.70  
  Purchase #2 $54.54   6.731%   $58.2111   $58.21   $58.20   $58.20  
  Purchase #3 $71.61   5.825%   $75.7813   $75.78   $75.80   $75.80  
  Purchase #4 $143.89   10.178%   $158.5351   $158.54   $158.55   $158.50  
  Purchase #5 $133.65   11.187%   $148.6014   $148.60   $148.60   $148.60  
  Purchase #6 $21.44   12.518%   $24.1239   $24.12   $24.10   $24.10  
  Purchase #7 $95.93   9.766%   $105.2985   $105.30   $105.30   $105.30  
  7 purchase totals = $577.04       $632.2110   $632.21   $632.20   $632.20