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 $163.32   12.785%   $184.2005   $184.20   $184.20   $184.20  
  Purchase #2 $38.97   6.190%   $41.3822   $41.38   $41.40   $41.40  
  Purchase #3 $64.37   5.247%   $67.7475   $67.75   $67.75   $67.70  
  Purchase #4 $58.54   3.845%   $60.7909   $60.79   $60.80   $60.80  
  Purchase #5 $192.89   10.583%   $213.3035   $213.30   $213.30   $213.30  
  Purchase #6 $101.41   8.834%   $110.3686   $110.37   $110.35   $110.40  
  Purchase #7 $75.59   13.676%   $85.9277   $85.93   $85.95   $85.90  
  7 purchase totals = $695.09       $763.7209   $763.72   $763.75   $763.70