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	$63.77	13.269%	$72.2316	$72.23	$72.25	$72.20
Purchase #2	$103.60	6.571%	$110.4076	$110.41	$110.40	$110.40
Purchase #3	$193.46	11.472%	$215.6537	$215.65	$215.65	$215.70
Purchase #4	$219.77	9.817%	$241.3448	$241.34	$241.35	$241.30
Purchase #5	$93.44	7.267%	$100.2303	$100.23	$100.25	$100.20
Purchase #6	$30.76	5.794%	$32.5422	$32.54	$32.55	$32.50
Purchase #7	$104.35	13.761%	$118.7096	$118.71	$118.70	$118.70
7 purchase totals =	$809.15		$891.1198	$891.11	$891.15	$891.00