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	$123.91	3.132%	$127.7909	$127.79	$127.80	$127.80
Purchase #2	$124.93	4.183%	$130.1558	$130.16	$130.15	$130.20
Purchase #3	$163.96	9.741%	$179.9313	$179.93	$179.95	$179.90
Purchase #4	$178.52	6.253%	$189.6829	$189.68	$189.70	$189.70
Purchase #5	$241.43	5.366%	$254.3851	$254.39	$254.40	$254.40
Purchase #6	$23.79	3.559%	$24.6367	$24.64	$24.65	$24.60
Purchase #7	$239.88	10.830%	$265.859	$265.86	$265.85	$265.90
7 purchase totals =	$1,096.42		$1,172.4417	$1,172.45	$1,172.50	$1,172.50