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 $214.61   13.819%   $244.267   $244.27   $244.25   $244.30  
  Purchase #2 $83.70   8.344%   $90.6839   $90.68   $90.70   $90.70  
  Purchase #3 $157.47   12.728%   $177.5128   $177.51   $177.50   $177.50  
  Purchase #4 $102.77   4.773%   $107.6752   $107.68   $107.70   $107.70  
  Purchase #5 $175.71   13.253%   $198.9968   $199.00   $199.00   $199.00  
  Purchase #6 $132.61   5.446%   $139.8319   $139.83   $139.85   $139.80  
  Purchase #7 $190.27   10.417%   $210.0904   $210.09   $210.10   $210.10  
  7 purchase totals = $1,057.14       $1,169.0580   $1,169.06   $1,169.10   $1,169.10