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 $175.94   10.116%   $193.7381   $193.74   $193.75   $193.70  
  Purchase #2 $239.64   3.841%   $248.8446   $248.84   $248.85   $248.80  
  Purchase #3 $153.96   3.369%   $159.1469   $159.15   $159.15   $159.10  
  Purchase #4 $197.67   12.244%   $221.8727   $221.87   $221.85   $221.90  
  Purchase #5 $241.90   4.552%   $252.9113   $252.91   $252.90   $252.90  
  Purchase #6 $146.69   8.403%   $159.0164   $159.02   $159.00   $159.00  
  Purchase #7 $12.56   10.844%   $13.922   $13.92   $13.90   $13.90  
  7 purchase totals = $1,168.36       $1,249.4520   $1,249.45   $1,249.40   $1,249.30