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 $83.96   4.863%   $88.043   $88.04   $88.05   $88.00  
  Purchase #2 $41.43   5.290%   $43.6216   $43.62   $43.60   $43.60  
  Purchase #3 $59.38   8.618%   $64.4974   $64.50   $64.50   $64.50  
  Purchase #4 $106.61   6.771%   $113.8286   $113.83   $113.85   $113.80  
  Purchase #5 $95.35   3.552%   $98.7368   $98.74   $98.75   $98.70  
  Purchase #6 $224.62   11.258%   $249.9077   $249.91   $249.90   $249.90  
  Purchase #7 $97.86   7.581%   $105.2788   $105.28   $105.30   $105.30  
  7 purchase totals = $709.21       $763.9139   $763.92   $763.95   $763.80