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 $54.88   9.752%   $60.2319   $60.23   $60.25   $60.20  
  Purchase #2 $142.67   11.297%   $158.7874   $158.79   $158.80   $158.80  
  Purchase #3 $233.88   8.382%   $253.4838   $253.48   $253.50   $253.50  
  Purchase #4 $83.86   4.575%   $87.6966   $87.70   $87.70   $87.70  
  Purchase #5 $31.41   8.442%   $34.0616   $34.06   $34.05   $34.10  
  Purchase #6 $224.61   10.576%   $248.3648   $248.36   $248.35   $248.40  
  Purchase #7 $233.44   8.163%   $252.4957   $252.50   $252.50   $252.50  
  7 purchase totals = $1,004.75       $1,095.1218   $1,095.12   $1,095.15   $1,095.20