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 $231.67   8.675%   $251.7674   $251.77   $251.75   $251.80  
  Purchase #2 $68.56   11.335%   $76.3313   $76.33   $76.35   $76.30  
  Purchase #3 $41.45   9.115%   $45.2282   $45.23   $45.25   $45.20  
  Purchase #4 $239.85   9.228%   $261.9834   $261.98   $262.00   $262.00  
  Purchase #5 $146.67   3.202%   $151.3664   $151.37   $151.35   $151.40  
  Purchase #6 $194.55   10.230%   $214.4525   $214.45   $214.45   $214.50  
  Purchase #7 $45.60   4.753%   $47.7674   $47.77   $47.75   $47.80  
  7 purchase totals = $968.35       $1,048.8966   $1,048.90   $1,048.90   $1,049.00