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 $213.67   12.607%   $240.6074   $240.61   $240.60   $240.60  
  Purchase #2 $98.66   4.813%   $103.4085   $103.41   $103.40   $103.40  
  Purchase #3 $221.38   12.297%   $248.6031   $248.60   $248.60   $248.60  
  Purchase #4 $203.63   13.308%   $230.7291   $230.73   $230.75   $230.70  
  Purchase #5 $228.75   8.242%   $247.6036   $247.60   $247.60   $247.60  
  Purchase #6 $236.36   13.571%   $268.4364   $268.44   $268.45   $268.40  
  Purchase #7 $26.85   3.257%   $27.7245   $27.72   $27.70   $27.70  
  7 purchase totals = $1,229.30       $1,367.1126   $1,367.11   $1,367.10   $1,367.00