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 $32.36   10.808%   $35.8575   $35.86   $35.85   $35.90  
  Purchase #2 $156.95   11.127%   $174.4138   $174.41   $174.40   $174.40  
  Purchase #3 $239.71   5.210%   $252.1989   $252.20   $252.20   $252.20  
  Purchase #4 $205.68   11.303%   $228.928   $228.93   $228.95   $228.90  
  Purchase #5 $62.37   8.791%   $67.8529   $67.85   $67.85   $67.90  
  Purchase #6 $250.94   4.647%   $262.6012   $262.60   $262.60   $262.60  
  Purchase #7 $210.94   4.784%   $221.0314   $221.03   $221.05   $221.00  
  7 purchase totals = $1,158.95       $1,242.8837   $1,242.88   $1,242.90   $1,242.90