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 $167.90   10.234%   $185.0829   $185.08   $185.10   $185.10  
  Purchase #2 $213.78   6.305%   $227.2588   $227.26   $227.25   $227.30  
  Purchase #3 $226.89   13.533%   $257.595   $257.60   $257.60   $257.60  
  Purchase #4 $241.70   13.513%   $274.3609   $274.36   $274.35   $274.40  
  Purchase #5 $70.37   4.421%   $73.4811   $73.48   $73.50   $73.50  
  Purchase #6 $151.92   11.410%   $169.2541   $169.25   $169.25   $169.30  
  Purchase #7 $98.85   9.509%   $108.2496   $108.25   $108.25   $108.20  
  7 purchase totals = $1,171.41       $1,295.2824   $1,295.28   $1,295.30   $1,295.40