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 $208.54   13.311%   $236.2988   $236.30   $236.30   $236.30  
  Purchase #2 $245.95   4.319%   $256.5726   $256.57   $256.55   $256.60  
  Purchase #3 $63.59   9.315%   $69.5134   $69.51   $69.50   $69.50  
  Purchase #4 $229.92   4.665%   $240.6458   $240.65   $240.65   $240.60  
  Purchase #5 $109.97   10.581%   $121.6059   $121.61   $121.60   $121.60  
  Purchase #6 $126.76   10.480%   $140.0444   $140.04   $140.05   $140.00  
  Purchase #7 $229.79   13.331%   $260.4233   $260.42   $260.40   $260.40  
  7 purchase totals = $1,214.52       $1,325.1042   $1,325.10   $1,325.05   $1,325.00