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 $244.85   6.196%   $260.0209   $260.02   $260.00   $260.00  
  Purchase #2 $126.97   5.309%   $133.7108   $133.71   $133.70   $133.70  
  Purchase #3 $114.51   4.137%   $119.2473   $119.25   $119.25   $119.20  
  Purchase #4 $65.50   4.461%   $68.422   $68.42   $68.40   $68.40  
  Purchase #5 $236.32   3.385%   $244.3194   $244.32   $244.30   $244.30  
  Purchase #6 $14.35   9.494%   $15.7124   $15.71   $15.70   $15.70  
  Purchase #7 $22.25   6.850%   $23.7741   $23.77   $23.75   $23.80  
  7 purchase totals = $824.75       $865.2069   $865.20   $865.10   $865.10