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 $85.83   12.288%   $96.3768   $96.38   $96.40   $96.40  
  Purchase #2 $161.32   11.718%   $180.2235   $180.22   $180.20   $180.20  
  Purchase #3 $160.84   3.141%   $165.892   $165.89   $165.90   $165.90  
  Purchase #4 $32.35   11.745%   $36.1495   $36.15   $36.15   $36.10  
  Purchase #5 $106.73   5.632%   $112.741   $112.74   $112.75   $112.70  
  Purchase #6 $57.49   7.463%   $61.7805   $61.78   $61.80   $61.80  
  Purchase #7 $245.90   8.505%   $266.8138   $266.81   $266.80   $266.80  
  7 purchase totals = $850.46       $919.9771   $919.97   $920.00   $919.90