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 $218.53   5.573%   $230.7087   $230.71   $230.70   $230.70  
  Purchase #2 $213.87   11.164%   $237.7464   $237.75   $237.75   $237.70  
  Purchase #3 $194.48   11.358%   $216.569   $216.57   $216.55   $216.60  
  Purchase #4 $107.96   12.193%   $121.1236   $121.12   $121.10   $121.10  
  Purchase #5 $6.63   11.557%   $7.3962   $7.40   $7.40   $7.40  
  Purchase #6 $136.33   8.861%   $148.4102   $148.41   $148.40   $148.40  
  Purchase #7 $104.47   9.449%   $114.3414   $114.34   $114.35   $114.30  
  7 purchase totals = $982.27       $1,076.2955   $1,076.30   $1,076.25   $1,076.20