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	$139.30	3.674%	$144.4179	$144.42	$144.40	$144.40
Purchase #2	$68.50	3.564%	$70.9413	$70.94	$70.95	$70.90
Purchase #3	$26.54	7.458%	$28.5194	$28.52	$28.50	$28.50
Purchase #4	$89.39	5.744%	$94.5246	$94.52	$94.50	$94.50
Purchase #5	$50.93	9.136%	$55.583	$55.58	$55.60	$55.60
Purchase #6	$223.36	13.396%	$253.2813	$253.28	$253.30	$253.30
Purchase #7	$166.35	3.419%	$172.0375	$172.04	$172.05	$172.00
7 purchase totals =	$764.37		$819.3050	$819.30	$819.30	$819.20