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 $190.44   8.684%   $206.9778   $206.98   $207.00   $207.00  
  Purchase #2 $158.59   10.700%   $175.5591   $175.56   $175.55   $175.60  
  Purchase #3 $241.85   4.696%   $253.2073   $253.21   $253.20   $253.20  
  Purchase #4 $178.90   9.168%   $195.3016   $195.30   $195.30   $195.30  
  Purchase #5 $130.54   3.390%   $134.9653   $134.97   $134.95   $135.00  
  Purchase #6 $95.53   6.137%   $101.3927   $101.39   $101.40   $101.40  
  Purchase #7 $221.79   6.626%   $236.4858   $236.49   $236.50   $236.50  
  7 purchase totals = $1,217.64       $1,303.8896   $1,303.90   $1,303.90   $1,304.00