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 $165.58   10.112%   $182.3234   $182.32   $182.30   $182.30  
  Purchase #2 $51.52   12.578%   $58.0002   $58.00   $58.00   $58.00  
  Purchase #3 $112.51   11.473%   $125.4183   $125.42   $125.40   $125.40  
  Purchase #4 $66.41   8.814%   $72.2634   $72.26   $72.25   $72.30  
  Purchase #5 $107.28   4.129%   $111.7096   $111.71   $111.70   $111.70  
  Purchase #6 $193.54   10.845%   $214.5294   $214.53   $214.55   $214.50  
  Purchase #7 $127.41   7.288%   $136.6956   $136.70   $136.70   $136.70  
  7 purchase totals = $824.25       $900.9399   $900.94   $900.90   $900.90