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 $192.36   4.797%   $201.5875   $201.59   $201.60   $201.60  
  Purchase #2 $184.76   6.102%   $196.0341   $196.03   $196.05   $196.00  
  Purchase #3 $214.93   10.195%   $236.8421   $236.84   $236.85   $236.80  
  Purchase #4 $44.73   6.465%   $47.6218   $47.62   $47.60   $47.60  
  Purchase #5 $111.67   13.177%   $126.3848   $126.38   $126.40   $126.40  
  Purchase #6 $119.25   5.263%   $125.5261   $125.53   $125.55   $125.50  
  Purchase #7 $68.46   5.662%   $72.3362   $72.34   $72.35   $72.30  
  7 purchase totals = $936.16       $1,006.3326   $1,006.33   $1,006.40   $1,006.20