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 $46.67   6.826%   $49.8557   $49.86   $49.85   $49.90  
  Purchase #2 $215.40   3.386%   $222.6934   $222.69   $222.70   $222.70  
  Purchase #3 $24.52   5.743%   $25.9282   $25.93   $25.95   $25.90  
  Purchase #4 $214.73   12.579%   $241.7409   $241.74   $241.75   $241.70  
  Purchase #5 $107.97   8.131%   $116.749   $116.75   $116.75   $116.70  
  Purchase #6 $90.52   7.290%   $97.1189   $97.12   $97.10   $97.10  
  Purchase #7 $227.26   10.266%   $250.5905   $250.59   $250.60   $250.60  
  7 purchase totals = $927.07       $1,004.6766   $1,004.68   $1,004.70   $1,004.60