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 $61.71   10.255%   $68.0384   $68.04   $68.05   $68.00  
  Purchase #2 $15.58   9.390%   $17.043   $17.04   $17.05   $17.00  
  Purchase #3 $131.44   8.198%   $142.2155   $142.22   $142.20   $142.20  
  Purchase #4 $72.86   12.823%   $82.2028   $82.20   $82.20   $82.20  
  Purchase #5 $25.78   3.211%   $26.6078   $26.61   $26.60   $26.60  
  Purchase #6 $13.31   4.212%   $13.8706   $13.87   $13.85   $13.90  
  Purchase #7 $20.78   10.756%   $23.0151   $23.02   $23.00   $23.00  
  7 purchase totals = $341.46       $372.9932   $373.00   $372.95   $372.90