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 $119.76   8.447%   $129.8761   $129.88   $129.90   $129.90  
  Purchase #2 $198.34   9.233%   $216.6527   $216.65   $216.65   $216.70  
  Purchase #3 $65.59   5.391%   $69.126   $69.13   $69.15   $69.10  
  Purchase #4 $57.56   12.628%   $64.8287   $64.83   $64.85   $64.80  
  Purchase #5 $225.57   9.612%   $247.2518   $247.25   $247.25   $247.30  
  Purchase #6 $105.89   9.607%   $116.0629   $116.06   $116.05   $116.10  
  Purchase #7 $113.83   3.290%   $117.575   $117.58   $117.60   $117.60  
  7 purchase totals = $886.54       $961.3732   $961.38   $961.45   $961.50