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 $238.31   3.787%   $247.3348   $247.33   $247.35   $247.30  
  Purchase #2 $32.97   8.235%   $35.6851   $35.69   $35.70   $35.70  
  Purchase #3 $35.52   3.752%   $36.8527   $36.85   $36.85   $36.90  
  Purchase #4 $58.59   7.373%   $62.9098   $62.91   $62.90   $62.90  
  Purchase #5 $86.25   7.234%   $92.4893   $92.49   $92.50   $92.50  
  Purchase #6 $204.71   4.727%   $214.3866   $214.39   $214.40   $214.40  
  Purchase #7 $10.34   12.574%   $11.6402   $11.64   $11.65   $11.60  
  7 purchase totals = $666.69       $701.2985   $701.30   $701.35   $701.30