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 $101.90   7.432%   $109.4732   $109.47   $109.45   $109.50  
  Purchase #2 $123.66   9.339%   $135.2086   $135.21   $135.20   $135.20  
  Purchase #3 $192.78   10.846%   $213.6889   $213.69   $213.70   $213.70  
  Purchase #4 $209.31   11.703%   $233.8055   $233.81   $233.80   $233.80  
  Purchase #5 $121.53   6.762%   $129.7479   $129.75   $129.75   $129.70  
  Purchase #6 $7.38   12.795%   $8.3243   $8.32   $8.30   $8.30  
  Purchase #7 $85.48   5.540%   $90.2156   $90.22   $90.20   $90.20  
  7 purchase totals = $842.04       $920.4640   $920.47   $920.40   $920.40