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 $32.31   6.601%   $34.4428   $34.44   $34.45   $34.40  
  Purchase #2 $173.74   8.338%   $188.2264   $188.23   $188.25   $188.20  
  Purchase #3 $155.48   4.346%   $162.2372   $162.24   $162.25   $162.20  
  Purchase #4 $62.26   12.321%   $69.9311   $69.93   $69.95   $69.90  
  Purchase #5 $208.47   4.781%   $218.437   $218.44   $218.45   $218.40  
  Purchase #6 $189.94   8.429%   $205.95   $205.95   $205.95   $206.00  
  Purchase #7 $48.78   13.817%   $55.5199   $55.52   $55.50   $55.50  
  7 purchase totals = $870.98       $934.7444   $934.75   $934.80   $934.60