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 $212.44   11.388%   $236.6327   $236.63   $236.65   $236.60  
  Purchase #2 $58.72   3.179%   $60.5867   $60.59   $60.60   $60.60  
  Purchase #3 $22.28   7.338%   $23.9149   $23.91   $23.90   $23.90  
  Purchase #4 $71.30   9.415%   $78.0129   $78.01   $78.00   $78.00  
  Purchase #5 $198.66   7.742%   $214.0403   $214.04   $214.05   $214.00  
  Purchase #6 $222.77   12.384%   $250.3578   $250.36   $250.35   $250.40  
  Purchase #7 $51.30   8.795%   $55.8118   $55.81   $55.80   $55.80  
  7 purchase totals = $837.47       $919.3571   $919.35   $919.35   $919.30