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	$111.60	6.767%	$119.152	$119.15	$119.15	$119.20
Purchase #2	$160.39	12.585%	$180.5751	$180.58	$180.60	$180.60
Purchase #3	$62.72	9.747%	$68.8333	$68.83	$68.85	$68.80
Purchase #4	$99.30	13.397%	$112.6032	$112.60	$112.60	$112.60
Purchase #5	$114.56	11.287%	$127.4904	$127.49	$127.50	$127.50
Purchase #6	$110.25	12.250%	$123.7556	$123.76	$123.75	$123.80
Purchase #7	$143.25	9.555%	$156.9375	$156.94	$156.95	$156.90
7 purchase totals =	$802.07		$889.3471	$889.35	$889.40	$889.40