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 $85.26   12.681%   $96.0718   $96.07   $96.05   $96.10  
  Purchase #2 $232.39   3.700%   $240.9884   $240.99   $241.00   $241.00  
  Purchase #3 $79.46   8.719%   $86.3881   $86.39   $86.40   $86.40  
  Purchase #4 $240.62   4.160%   $250.6298   $250.63   $250.65   $250.60  
  Purchase #5 $204.95   11.582%   $228.6873   $228.69   $228.70   $228.70  
  Purchase #6 $171.25   12.553%   $192.747   $192.75   $192.75   $192.70  
  Purchase #7 $97.27   5.618%   $102.7346   $102.73   $102.75   $102.70  
  7 purchase totals = $1,111.20       $1,198.2470   $1,198.25   $1,198.30   $1,198.20