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 $228.48   8.543%   $247.999   $248.00   $248.00   $248.00  
  Purchase #2 $242.85   8.231%   $262.839   $262.84   $262.85   $262.80  
  Purchase #3 $206.90   4.866%   $216.9678   $216.97   $216.95   $217.00  
  Purchase #4 $169.56   10.207%   $186.867   $186.87   $186.85   $186.90  
  Purchase #5 $151.45   10.452%   $167.2796   $167.28   $167.30   $167.30  
  Purchase #6 $85.74   3.710%   $88.921   $88.92   $88.90   $88.90  
  Purchase #7 $165.41   7.117%   $177.1822   $177.18   $177.20   $177.20  
  7 purchase totals = $1,250.39       $1,348.0556   $1,348.06   $1,348.05   $1,348.10