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 $205.43   12.105%   $230.2973   $230.30   $230.30   $230.30  
  Purchase #2 $159.78   7.415%   $171.6277   $171.63   $171.65   $171.60  
  Purchase #3 $58.70   3.696%   $60.8696   $60.87   $60.85   $60.90  
  Purchase #4 $40.69   4.576%   $42.552   $42.55   $42.55   $42.60  
  Purchase #5 $125.80   5.821%   $133.1228   $133.12   $133.10   $133.10  
  Purchase #6 $23.27   3.139%   $24.0004   $24.00   $24.00   $24.00  
  Purchase #7 $63.77   5.441%   $67.2397   $67.24   $67.25   $67.20  
  7 purchase totals = $677.44       $729.7095   $729.71   $729.70   $729.70