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	$71.38	12.851%	$80.553	$80.55	$80.55	$80.60
Purchase #2	$35.58	5.201%	$37.4305	$37.43	$37.45	$37.40
Purchase #3	$208.25	3.530%	$215.6012	$215.60	$215.60	$215.60
Purchase #4	$156.97	10.574%	$173.568	$173.57	$173.55	$173.60
Purchase #5	$16.65	11.488%	$18.5628	$18.56	$18.55	$18.60
Purchase #6	$178.70	13.181%	$202.2544	$202.25	$202.25	$202.30
Purchase #7	$30.54	5.806%	$32.3132	$32.31	$32.30	$32.30
7 purchase totals =	$698.07		$760.2831	$760.27	$760.25	$760.40