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 $204.29   12.316%   $229.4504   $229.45   $229.45   $229.50  
  Purchase #2 $205.76   5.331%   $216.7291   $216.73   $216.75   $216.70  
  Purchase #3 $150.90   4.304%   $157.3947   $157.39   $157.40   $157.40  
  Purchase #4 $246.26   8.401%   $266.9483   $266.95   $266.95   $266.90  
  Purchase #5 $49.37   6.630%   $52.6432   $52.64   $52.65   $52.60  
  Purchase #6 $206.41   3.546%   $213.7293   $213.73   $213.75   $213.70  
  Purchase #7 $60.68   6.252%   $64.4737   $64.47   $64.45   $64.50  
  7 purchase totals = $1,123.67       $1,201.3687   $1,201.36   $1,201.40   $1,201.30