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 $98.36   8.631%   $106.8495   $106.85   $106.85   $106.80  
  Purchase #2 $149.93   8.609%   $162.8375   $162.84   $162.85   $162.80  
  Purchase #3 $119.99   6.455%   $127.7354   $127.74   $127.75   $127.70  
  Purchase #4 $101.34   8.368%   $109.8201   $109.82   $109.80   $109.80  
  Purchase #5 $68.80   4.781%   $72.0893   $72.09   $72.10   $72.10  
  Purchase #6 $58.70   12.537%   $66.0592   $66.06   $66.05   $66.10  
  Purchase #7 $171.45   8.471%   $185.9735   $185.97   $185.95   $186.00  
  7 purchase totals = $768.57       $831.3645   $831.37   $831.35   $831.30