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 $85.25   11.799%   $95.3086   $95.31   $95.30   $95.30  
  Purchase #2 $186.82   13.325%   $211.7138   $211.71   $211.70   $211.70  
  Purchase #3 $5.95   4.728%   $6.2313   $6.23   $6.25   $6.20  
  Purchase #4 $191.40   9.169%   $208.9495   $208.95   $208.95   $208.90  
  Purchase #5 $216.98   7.783%   $233.8676   $233.87   $233.85   $233.90  
  Purchase #6 $163.31   13.366%   $185.138   $185.14   $185.15   $185.10  
  Purchase #7 $45.97   13.601%   $52.2224   $52.22   $52.20   $52.20  
  7 purchase totals = $895.68       $993.4312   $993.43   $993.40   $993.30