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 $196.86   11.769%   $220.0285   $220.03   $220.05   $220.00  
  Purchase #2 $33.96   11.538%   $37.8783   $37.88   $37.90   $37.90  
  Purchase #3 $182.65   5.103%   $191.9706   $191.97   $191.95   $192.00  
  Purchase #4 $151.89   10.576%   $167.9539   $167.95   $167.95   $168.00  
  Purchase #5 $113.87   7.159%   $122.022   $122.02   $122.00   $122.00  
  Purchase #6 $168.89   5.763%   $178.6231   $178.62   $178.60   $178.60  
  Purchase #7 $112.68   10.779%   $124.8258   $124.83   $124.85   $124.80  
  7 purchase totals = $960.80       $1,043.3022   $1,043.30   $1,043.30   $1,043.30