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 $50.97   11.201%   $56.6791   $56.68   $56.70   $56.70  
  Purchase #2 $234.84   5.579%   $247.9417   $247.94   $247.95   $247.90  
  Purchase #3 $14.94   3.242%   $15.4244   $15.42   $15.40   $15.40  
  Purchase #4 $65.47   6.501%   $69.7262   $69.73   $69.75   $69.70  
  Purchase #5 $111.77   3.441%   $115.616   $115.62   $115.60   $115.60  
  Purchase #6 $74.72   10.533%   $82.5903   $82.59   $82.60   $82.60  
  Purchase #7 $178.40   5.642%   $188.4653   $188.47   $188.45   $188.50  
  7 purchase totals = $731.11       $776.4430   $776.45   $776.45   $776.40