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 $164.86   6.406%   $175.4209   $175.42   $175.40   $175.40  
  Purchase #2 $211.99   11.391%   $236.1378   $236.14   $236.15   $236.10  
  Purchase #3 $46.75   5.414%   $49.281   $49.28   $49.30   $49.30  
  Purchase #4 $230.58   13.844%   $262.5015   $262.50   $262.50   $262.50  
  Purchase #5 $156.61   12.322%   $175.9075   $175.91   $175.90   $175.90  
  Purchase #6 $118.93   11.523%   $132.6343   $132.63   $132.65   $132.60  
  Purchase #7 $147.83   13.554%   $167.8669   $167.87   $167.85   $167.90  
  7 purchase totals = $1,077.55       $1,199.7499   $1,199.75   $1,199.75   $1,199.70