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 $65.37   6.445%   $69.5831   $69.58   $69.60   $69.60  
  Purchase #2 $97.36   7.378%   $104.5432   $104.54   $104.55   $104.50  
  Purchase #3 $56.88   8.452%   $61.6875   $61.69   $61.70   $61.70  
  Purchase #4 $163.91   9.305%   $179.1618   $179.16   $179.15   $179.20  
  Purchase #5 $87.77   5.675%   $92.7509   $92.75   $92.75   $92.80  
  Purchase #6 $204.42   5.121%   $214.8883   $214.89   $214.90   $214.90  
  Purchase #7 $125.49   11.359%   $139.7444   $139.74   $139.75   $139.70  
  7 purchase totals = $801.20       $862.3592   $862.35   $862.40   $862.40