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 $30.91   13.514%   $35.0872   $35.09   $35.10   $35.10  
  Purchase #2 $214.60   12.812%   $242.0946   $242.09   $242.10   $242.10  
  Purchase #3 $106.55   6.225%   $113.1827   $113.18   $113.20   $113.20  
  Purchase #4 $24.94   3.575%   $25.8316   $25.83   $25.85   $25.80  
  Purchase #5 $192.81   11.275%   $214.5493   $214.55   $214.55   $214.50  
  Purchase #6 $238.87   9.438%   $261.4146   $261.41   $261.40   $261.40  
  Purchase #7 $70.52   9.873%   $77.4824   $77.48   $77.50   $77.50  
  7 purchase totals = $879.20       $969.6424   $969.63   $969.70   $969.60