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 $116.55   9.261%   $127.3437   $127.34   $127.35   $127.30  
  Purchase #2 $72.85   4.792%   $76.341   $76.34   $76.35   $76.30  
  Purchase #3 $115.49   9.870%   $126.8889   $126.89   $126.90   $126.90  
  Purchase #4 $138.58   13.367%   $157.104   $157.10   $157.10   $157.10  
  Purchase #5 $161.81   8.669%   $175.8373   $175.84   $175.85   $175.80  
  Purchase #6 $119.60   8.374%   $129.6153   $129.62   $129.60   $129.60  
  Purchase #7 $107.96   8.520%   $117.1582   $117.16   $117.15   $117.20  
  7 purchase totals = $832.84       $910.2884   $910.29   $910.30   $910.20