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 $247.33   7.159%   $265.0364   $265.04   $265.05   $265.00  
  Purchase #2 $21.67   6.619%   $23.1043   $23.10   $23.10   $23.10  
  Purchase #3 $164.74   3.639%   $170.7349   $170.73   $170.75   $170.70  
  Purchase #4 $190.67   8.299%   $206.4937   $206.49   $206.50   $206.50  
  Purchase #5 $166.85   10.763%   $184.8081   $184.81   $184.80   $184.80  
  Purchase #6 $133.74   8.557%   $145.1841   $145.18   $145.20   $145.20  
  Purchase #7 $34.45   10.672%   $38.1265   $38.13   $38.15   $38.10  
  7 purchase totals = $959.45       $1,033.4880   $1,033.48   $1,033.55   $1,033.40