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 $206.75   8.378%   $224.0715   $224.07   $224.05   $224.10  
  Purchase #2 $55.30   3.789%   $57.3953   $57.40   $57.40   $57.40  
  Purchase #3 $154.57   8.559%   $167.7996   $167.80   $167.80   $167.80  
  Purchase #4 $101.97   12.420%   $114.6347   $114.63   $114.65   $114.60  
  Purchase #5 $102.48   13.303%   $116.1129   $116.11   $116.10   $116.10  
  Purchase #6 $239.87   9.405%   $262.4298   $262.43   $262.45   $262.40  
  Purchase #7 $132.64   7.817%   $143.0085   $143.01   $143.00   $143.00  
  7 purchase totals = $993.58       $1,085.4523   $1,085.45   $1,085.45   $1,085.40