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 $215.90   11.336%   $240.3744   $240.37   $240.35   $240.40  
  Purchase #2 $191.46   7.683%   $206.1699   $206.17   $206.15   $206.20  
  Purchase #3 $119.54   7.784%   $128.845   $128.85   $128.85   $128.80  
  Purchase #4 $105.60   9.721%   $115.8654   $115.87   $115.85   $115.90  
  Purchase #5 $127.35   5.119%   $133.869   $133.87   $133.85   $133.90  
  Purchase #6 $57.68   9.703%   $63.2767   $63.28   $63.30   $63.30  
  Purchase #7 $248.46   5.693%   $262.6048   $262.60   $262.60   $262.60  
  7 purchase totals = $1,065.99       $1,151.0052   $1,151.01   $1,150.95   $1,151.10