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 $60.89   6.825%   $65.0457   $65.05   $65.05   $65.00  
  Purchase #2 $41.27   3.266%   $42.6179   $42.62   $42.60   $42.60  
  Purchase #3 $146.92   3.244%   $151.6861   $151.69   $151.70   $151.70  
  Purchase #4 $116.34   13.802%   $132.3972   $132.40   $132.40   $132.40  
  Purchase #5 $104.68   13.188%   $118.4852   $118.49   $118.50   $118.50  
  Purchase #6 $171.87   3.178%   $177.332   $177.33   $177.35   $177.30  
  Purchase #7 $118.99   10.162%   $131.0818   $131.08   $131.10   $131.10  
  7 purchase totals = $760.96       $818.6459   $818.66   $818.70   $818.60