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 $226.41   5.711%   $239.3403   $239.34   $239.35   $239.30  
  Purchase #2 $174.50   11.235%   $194.1051   $194.11   $194.10   $194.10  
  Purchase #3 $62.42   3.183%   $64.4068   $64.41   $64.40   $64.40  
  Purchase #4 $178.26   10.676%   $197.291   $197.29   $197.30   $197.30  
  Purchase #5 $125.83   11.494%   $140.2929   $140.29   $140.30   $140.30  
  Purchase #6 $122.46   3.811%   $127.127   $127.13   $127.15   $127.10  
  Purchase #7 $135.44   5.218%   $142.5073   $142.51   $142.50   $142.50  
  7 purchase totals = $1,025.32       $1,105.0704   $1,105.08   $1,105.10   $1,105.00