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 $66.63   10.617%   $73.7041   $73.70   $73.70   $73.70  
  Purchase #2 $201.42   4.643%   $210.7719   $210.77   $210.75   $210.80  
  Purchase #3 $125.27   4.269%   $130.6178   $130.62   $130.60   $130.60  
  Purchase #4 $242.84   11.489%   $270.7399   $270.74   $270.75   $270.70  
  Purchase #5 $112.68   6.285%   $119.7619   $119.76   $119.75   $119.80  
  Purchase #6 $158.72   8.105%   $171.5843   $171.58   $171.60   $171.60  
  Purchase #7 $22.87   7.105%   $24.4949   $24.49   $24.50   $24.50  
  7 purchase totals = $930.43       $1,001.6748   $1,001.66   $1,001.65   $1,001.70