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 $105.79   11.697%   $118.1643   $118.16   $118.15   $118.20  
  Purchase #2 $126.29   5.664%   $133.4431   $133.44   $133.45   $133.40  
  Purchase #3 $157.59   8.698%   $171.2972   $171.30   $171.30   $171.30  
  Purchase #4 $53.72   5.562%   $56.7079   $56.71   $56.70   $56.70  
  Purchase #5 $250.62   10.716%   $277.4764   $277.48   $277.50   $277.50  
  Purchase #6 $229.48   9.713%   $251.7694   $251.77   $251.75   $251.80  
  Purchase #7 $196.45   10.165%   $216.4191   $216.42   $216.40   $216.40  
  7 purchase totals = $1,119.94       $1,225.2774   $1,225.28   $1,225.25   $1,225.30