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 $196.58   12.305%   $220.7692   $220.77   $220.75   $220.80  
  Purchase #2 $141.57   4.365%   $147.7495   $147.75   $147.75   $147.70  
  Purchase #3 $248.90   8.447%   $269.9246   $269.92   $269.90   $269.90  
  Purchase #4 $199.65   7.786%   $215.1947   $215.19   $215.20   $215.20  
  Purchase #5 $23.25   12.873%   $26.243   $26.24   $26.25   $26.20  
  Purchase #6 $232.91   11.223%   $259.0495   $259.05   $259.05   $259.00  
  Purchase #7 $118.68   12.401%   $133.3975   $133.40   $133.40   $133.40  
  7 purchase totals = $1,161.54       $1,272.3280   $1,272.32   $1,272.30   $1,272.20