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 $185.76   12.257%   $208.5286   $208.53   $208.55   $208.50  
  Purchase #2 $175.57   11.107%   $195.0706   $195.07   $195.05   $195.10  
  Purchase #3 $237.78   12.699%   $267.9757   $267.98   $268.00   $268.00  
  Purchase #4 $181.29   5.578%   $191.4024   $191.40   $191.40   $191.40  
  Purchase #5 $37.42   11.459%   $41.708   $41.71   $41.70   $41.70  
  Purchase #6 $143.59   12.218%   $161.1338   $161.13   $161.15   $161.10  
  Purchase #7 $142.44   12.870%   $160.772   $160.77   $160.75   $160.80  
  7 purchase totals = $1,103.85       $1,226.5911   $1,226.59   $1,226.60   $1,226.60