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 $203.25   11.251%   $226.1177   $226.12   $226.10   $226.10  
  Purchase #2 $65.86   5.692%   $69.6088   $69.61   $69.60   $69.60  
  Purchase #3 $113.67   7.349%   $122.0236   $122.02   $122.00   $122.00  
  Purchase #4 $59.64   8.219%   $64.5418   $64.54   $64.55   $64.50  
  Purchase #5 $53.43   12.614%   $60.1697   $60.17   $60.15   $60.20  
  Purchase #6 $127.46   11.726%   $142.406   $142.41   $142.40   $142.40  
  Purchase #7 $98.92   5.617%   $104.4763   $104.48   $104.50   $104.50  
  7 purchase totals = $722.23       $789.3439   $789.35   $789.30   $789.30