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 $44.94   3.130%   $46.3466   $46.35   $46.35   $46.30  
  Purchase #2 $94.56   7.807%   $101.9423   $101.94   $101.95   $101.90  
  Purchase #3 $15.50   6.182%   $16.4582   $16.46   $16.45   $16.50  
  Purchase #4 $219.77   5.261%   $231.3321   $231.33   $231.35   $231.30  
  Purchase #5 $192.47   5.582%   $203.2137   $203.21   $203.20   $203.20  
  Purchase #6 $117.77   12.507%   $132.4995   $132.50   $132.50   $132.50  
  Purchase #7 $93.90   13.697%   $106.7615   $106.76   $106.75   $106.80  
  7 purchase totals = $778.91       $838.5539   $838.55   $838.55   $838.50