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	$80.38	11.722%	$89.8021	$89.80	$89.80	$89.80
Purchase #2	$56.92	11.662%	$63.558	$63.56	$63.55	$63.60
Purchase #3	$131.94	9.731%	$144.7791	$144.78	$144.80	$144.80
Purchase #4	$223.37	7.762%	$240.708	$240.71	$240.70	$240.70
Purchase #5	$74.60	5.514%	$78.7134	$78.71	$78.70	$78.70
Purchase #6	$240.96	13.621%	$273.7812	$273.78	$273.80	$273.80
Purchase #7	$5.94	9.681%	$6.5151	$6.52	$6.50	$6.50
7 purchase totals =	$814.11		$897.8569	$897.86	$897.85	$897.90