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 $208.69   8.250%   $225.9069   $225.91   $225.90   $225.90  
  Purchase #2 $82.27   7.857%   $88.734   $88.73   $88.75   $88.70  
  Purchase #3 $33.88   7.742%   $36.503   $36.50   $36.50   $36.50  
  Purchase #4 $85.86   7.686%   $92.4592   $92.46   $92.45   $92.50  
  Purchase #5 $216.47   11.650%   $241.6888   $241.69   $241.70   $241.70  
  Purchase #6 $119.35   4.846%   $125.1337   $125.13   $125.15   $125.10  
  Purchase #7 $194.73   6.439%   $207.2687   $207.27   $207.25   $207.30  
  7 purchase totals = $941.25       $1,017.6943   $1,017.69   $1,017.70   $1,017.70