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 $53.57   5.172%   $56.3406   $56.34   $56.35   $56.30  
  Purchase #2 $96.93   7.391%   $104.0941   $104.09   $104.10   $104.10  
  Purchase #3 $159.76   6.671%   $170.4176   $170.42   $170.40   $170.40  
  Purchase #4 $27.51   8.134%   $29.7477   $29.75   $29.75   $29.70  
  Purchase #5 $161.93   10.219%   $178.4776   $178.48   $178.50   $178.50  
  Purchase #6 $149.74   7.626%   $161.1592   $161.16   $161.15   $161.20  
  Purchase #7 $95.68   6.655%   $102.0475   $102.05   $102.05   $102.00  
  7 purchase totals = $745.12       $802.2843   $802.29   $802.30   $802.20