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 $175.88   5.742%   $185.979   $185.98   $186.00   $186.00  
  Purchase #2 $139.41   10.379%   $153.8794   $153.88   $153.90   $153.90  
  Purchase #3 $218.92   5.577%   $231.1292   $231.13   $231.15   $231.10  
  Purchase #4 $44.25   4.559%   $46.2674   $46.27   $46.25   $46.30  
  Purchase #5 $98.74   9.297%   $107.9199   $107.92   $107.90   $107.90  
  Purchase #6 $161.98   5.438%   $170.7885   $170.79   $170.80   $170.80  
  Purchase #7 $230.73   8.694%   $250.7897   $250.79   $250.80   $250.80  
  7 purchase totals = $1,069.91       $1,146.7531   $1,146.76   $1,146.80   $1,146.80