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 $241.82   11.693%   $270.096   $270.10   $270.10   $270.10  
  Purchase #2 $182.81   6.649%   $194.965   $194.97   $194.95   $195.00  
  Purchase #3 $34.44   10.662%   $38.112   $38.11   $38.10   $38.10  
  Purchase #4 $28.30   5.401%   $29.8285   $29.83   $29.85   $29.80  
  Purchase #5 $248.63   7.119%   $266.33   $266.33   $266.35   $266.30  
  Purchase #6 $248.89   5.374%   $262.2653   $262.27   $262.25   $262.30  
  Purchase #7 $87.28   7.181%   $93.5476   $93.55   $93.55   $93.50  
  7 purchase totals = $1,072.17       $1,155.1444   $1,155.16   $1,155.15   $1,155.10