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 $240.75   13.752%   $273.8579   $273.86   $273.85   $273.90  
  Purchase #2 $218.74   8.491%   $237.3132   $237.31   $237.30   $237.30  
  Purchase #3 $34.69   4.707%   $36.3229   $36.32   $36.30   $36.30  
  Purchase #4 $226.53   5.843%   $239.7661   $239.77   $239.75   $239.80  
  Purchase #5 $103.39   9.207%   $112.9091   $112.91   $112.90   $112.90  
  Purchase #6 $191.84   4.241%   $199.9759   $199.98   $200.00   $200.00  
  Purchase #7 $156.87   5.132%   $164.9206   $164.92   $164.90   $164.90  
  7 purchase totals = $1,172.81       $1,265.0657   $1,265.07   $1,265.00   $1,265.10