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 $149.49   8.832%   $162.693   $162.69   $162.70   $162.70  
  Purchase #2 $14.77   12.431%   $16.6061   $16.61   $16.60   $16.60  
  Purchase #3 $176.88   8.757%   $192.3694   $192.37   $192.35   $192.40  
  Purchase #4 $90.42   5.282%   $95.196   $95.20   $95.20   $95.20  
  Purchase #5 $164.76   9.691%   $180.7269   $180.73   $180.75   $180.70  
  Purchase #6 $45.59   12.297%   $51.1962   $51.20   $51.20   $51.20  
  Purchase #7 $94.86   3.198%   $97.8936   $97.89   $97.90   $97.90  
  7 purchase totals = $736.77       $796.6812   $796.69   $796.70   $796.70