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 $61.91   13.873%   $70.4988   $70.50   $70.50   $70.50  
  Purchase #2 $30.90   5.271%   $32.5287   $32.53   $32.55   $32.50  
  Purchase #3 $102.95   10.356%   $113.6115   $113.61   $113.60   $113.60  
  Purchase #4 $161.54   12.814%   $182.2397   $182.24   $182.25   $182.20  
  Purchase #5 $200.93   9.865%   $220.7517   $220.75   $220.75   $220.80  
  Purchase #6 $142.94   9.775%   $156.9124   $156.91   $156.90   $156.90  
  Purchase #7 $35.25   11.608%   $39.3418   $39.34   $39.35   $39.30  
  7 purchase totals = $736.42       $815.8846   $815.88   $815.90   $815.80