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 $14.81   11.257%   $16.4772   $16.48   $16.50   $16.50  
  Purchase #2 $216.61   5.154%   $227.7741   $227.77   $227.75   $227.80  
  Purchase #3 $249.75   9.512%   $273.5062   $273.51   $273.50   $273.50  
  Purchase #4 $89.58   12.832%   $101.0749   $101.07   $101.05   $101.10  
  Purchase #5 $130.39   11.540%   $145.437   $145.44   $145.45   $145.40  
  Purchase #6 $184.41   13.304%   $208.9439   $208.94   $208.95   $208.90  
  Purchase #7 $246.98   8.505%   $267.9856   $267.99   $268.00   $268.00  
  7 purchase totals = $1,132.53       $1,241.1989   $1,241.20   $1,241.20   $1,241.20