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 $63.71   3.203%   $65.7506   $65.75   $65.75   $65.80  
  Purchase #2 $100.96   12.258%   $113.3357   $113.34   $113.35   $113.30  
  Purchase #3 $16.54   8.476%   $17.9419   $17.94   $17.95   $17.90  
  Purchase #4 $158.54   3.232%   $163.664   $163.66   $163.65   $163.70  
  Purchase #5 $34.81   6.659%   $37.128   $37.13   $37.15   $37.10  
  Purchase #6 $163.76   12.831%   $184.772   $184.77   $184.75   $184.80  
  Purchase #7 $195.69   9.669%   $214.6113   $214.61   $214.60   $214.60  
  7 purchase totals = $734.01       $797.2035   $797.20   $797.20   $797.20