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 $29.41   4.337%   $30.6855   $30.69   $30.70   $30.70  
  Purchase #2 $77.51   6.680%   $82.6877   $82.69   $82.70   $82.70  
  Purchase #3 $18.91   12.450%   $21.2643   $21.26   $21.25   $21.30  
  Purchase #4 $229.78   11.333%   $255.821   $255.82   $255.80   $255.80  
  Purchase #5 $178.97   5.676%   $189.1283   $189.13   $189.15   $189.10  
  Purchase #6 $27.73   9.692%   $30.4176   $30.42   $30.40   $30.40  
  Purchase #7 $124.88   10.540%   $138.0424   $138.04   $138.05   $138.00  
  7 purchase totals = $687.19       $748.0468   $748.05   $748.05   $748.00