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 $224.65   5.658%   $237.3607   $237.36   $237.35   $237.40  
  Purchase #2 $123.73   10.564%   $136.8008   $136.80   $136.80   $136.80  
  Purchase #3 $144.95   8.434%   $157.1751   $157.18   $157.20   $157.20  
  Purchase #4 $31.46   12.214%   $35.3025   $35.30   $35.30   $35.30  
  Purchase #5 $73.53   13.164%   $83.2095   $83.21   $83.20   $83.20  
  Purchase #6 $61.41   5.261%   $64.6408   $64.64   $64.65   $64.60  
  Purchase #7 $229.34   10.719%   $253.923   $253.92   $253.90   $253.90  
  7 purchase totals = $889.07       $968.4124   $968.41   $968.40   $968.40