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 $191.44   11.372%   $213.2106   $213.21   $213.20   $213.20  
  Purchase #2 $157.70   6.491%   $167.9363   $167.94   $167.95   $167.90  
  Purchase #3 $195.28   3.825%   $202.7495   $202.75   $202.75   $202.70  
  Purchase #4 $196.94   8.724%   $214.121   $214.12   $214.10   $214.10  
  Purchase #5 $127.56   4.860%   $133.7594   $133.76   $133.75   $133.80  
  Purchase #6 $112.97   5.266%   $118.919   $118.92   $118.90   $118.90  
  Purchase #7 $173.97   9.803%   $191.0243   $191.02   $191.00   $191.00  
  7 purchase totals = $1,155.86       $1,241.7201   $1,241.72   $1,241.65   $1,241.60