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 $239.67   11.827%   $268.0158   $268.02   $268.00   $268.00  
  Purchase #2 $66.48   5.377%   $70.0546   $70.05   $70.05   $70.10  
  Purchase #3 $219.58   13.129%   $248.4087   $248.41   $248.40   $248.40  
  Purchase #4 $89.85   10.155%   $98.9743   $98.97   $98.95   $99.00  
  Purchase #5 $173.53   5.521%   $183.1106   $183.11   $183.10   $183.10  
  Purchase #6 $233.36   7.277%   $250.3416   $250.34   $250.35   $250.30  
  Purchase #7 $209.79   13.171%   $237.4214   $237.42   $237.40   $237.40  
  7 purchase totals = $1,232.26       $1,356.3270   $1,356.32   $1,356.25   $1,356.30