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 $92.82   4.327%   $96.8363   $96.84   $96.85   $96.80  
  Purchase #2 $96.39   8.868%   $104.9379   $104.94   $104.95   $104.90  
  Purchase #3 $77.64   7.214%   $83.2409   $83.24   $83.25   $83.20  
  Purchase #4 $26.47   6.325%   $28.1442   $28.14   $28.15   $28.10  
  Purchase #5 $108.49   8.541%   $117.7561   $117.76   $117.75   $117.80  
  Purchase #6 $108.46   6.486%   $115.4947   $115.49   $115.50   $115.50  
  Purchase #7 $55.66   3.161%   $57.4194   $57.42   $57.40   $57.40  
  7 purchase totals = $565.93       $603.8295   $603.83   $603.85   $603.70