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 $208.98   9.707%   $229.2657   $229.27   $229.25   $229.30  
  Purchase #2 $177.25   10.758%   $196.3186   $196.32   $196.30   $196.30  
  Purchase #3 $206.28   4.737%   $216.0515   $216.05   $216.05   $216.10  
  Purchase #4 $191.99   5.246%   $202.0618   $202.06   $202.05   $202.10  
  Purchase #5 $103.74   12.482%   $116.6888   $116.69   $116.70   $116.70  
  Purchase #6 $129.72   13.130%   $146.7522   $146.75   $146.75   $146.80  
  Purchase #7 $58.27   13.577%   $66.1813   $66.18   $66.20   $66.20  
  7 purchase totals = $1,076.23       $1,173.3199   $1,173.32   $1,173.30   $1,173.50