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 $235.77   6.293%   $250.607   $250.61   $250.60   $250.60  
  Purchase #2 $209.91   3.821%   $217.9307   $217.93   $217.95   $217.90  
  Purchase #3 $85.81   11.290%   $95.4979   $95.50   $95.50   $95.50  
  Purchase #4 $175.54   8.841%   $191.0595   $191.06   $191.05   $191.10  
  Purchase #5 $249.76   8.579%   $271.1869   $271.19   $271.20   $271.20  
  Purchase #6 $31.55   8.163%   $34.1254   $34.13   $34.15   $34.10  
  Purchase #7 $128.45   9.176%   $140.2366   $140.24   $140.25   $140.20  
  7 purchase totals = $1,116.79       $1,200.6440   $1,200.66   $1,200.70   $1,200.60