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 $171.70   7.863%   $185.2008   $185.20   $185.20   $185.20  
  Purchase #2 $96.26   8.483%   $104.4257   $104.43   $104.45   $104.40  
  Purchase #3 $151.59   6.781%   $161.8693   $161.87   $161.85   $161.90  
  Purchase #4 $133.60   13.597%   $151.7656   $151.77   $151.75   $151.80  
  Purchase #5 $186.35   3.780%   $193.394   $193.39   $193.40   $193.40  
  Purchase #6 $213.87   11.208%   $237.8405   $237.84   $237.85   $237.80  
  Purchase #7 $107.89   6.121%   $114.4939   $114.49   $114.50   $114.50  
  7 purchase totals = $1,061.26       $1,148.9898   $1,148.99   $1,149.00   $1,149.00