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 $201.92   11.524%   $225.1893   $225.19   $225.20   $225.20  
  Purchase #2 $51.63   6.668%   $55.0727   $55.07   $55.05   $55.10  
  Purchase #3 $175.84   6.176%   $186.6999   $186.70   $186.70   $186.70  
  Purchase #4 $100.98   13.572%   $114.685   $114.69   $114.70   $114.70  
  Purchase #5 $106.46   9.551%   $116.628   $116.63   $116.65   $116.60  
  Purchase #6 $116.90   6.698%   $124.73   $124.73   $124.75   $124.70  
  Purchase #7 $180.60   5.363%   $190.2856   $190.29   $190.30   $190.30  
  7 purchase totals = $934.33       $1,013.2905   $1,013.30   $1,013.35   $1,013.30