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 $65.50   4.534%   $68.4698   $68.47   $68.45   $68.50  
  Purchase #2 $64.38   6.171%   $68.3529   $68.35   $68.35   $68.40  
  Purchase #3 $41.51   11.603%   $46.3264   $46.33   $46.35   $46.30  
  Purchase #4 $35.63   8.541%   $38.6732   $38.67   $38.65   $38.70  
  Purchase #5 $37.50   11.677%   $41.8789   $41.88   $41.90   $41.90  
  Purchase #6 $219.91   5.374%   $231.728   $231.73   $231.75   $231.70  
  Purchase #7 $208.25   6.271%   $221.3094   $221.31   $221.30   $221.30  
  7 purchase totals = $672.68       $716.7386   $716.74   $716.75   $716.80