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 $249.58   6.591%   $266.0298   $266.03   $266.05   $266.00  
  Purchase #2 $121.80   12.732%   $137.3076   $137.31   $137.30   $137.30  
  Purchase #3 $226.29   9.664%   $248.1587   $248.16   $248.15   $248.20  
  Purchase #4 $67.97   4.820%   $71.2462   $71.25   $71.25   $71.20  
  Purchase #5 $183.74   4.493%   $191.9954   $192.00   $192.00   $192.00  
  Purchase #6 $166.76   4.420%   $174.1308   $174.13   $174.15   $174.10  
  Purchase #7 $118.64   3.207%   $122.4448   $122.44   $122.45   $122.40  
  7 purchase totals = $1,134.78       $1,211.3133   $1,211.32   $1,211.35   $1,211.20