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	$104.35	6.170%	$110.7884	$110.79	$110.80	$110.80
Purchase #2	$55.45	5.333%	$58.4071	$58.41	$58.40	$58.40
Purchase #3	$32.50	6.436%	$34.5917	$34.59	$34.60	$34.60
Purchase #4	$200.27	11.435%	$223.1709	$223.17	$223.15	$223.20
Purchase #5	$241.53	12.538%	$271.813	$271.81	$271.80	$271.80
Purchase #6	$68.79	13.723%	$78.2301	$78.23	$78.25	$78.20
Purchase #7	$29.67	9.827%	$32.5857	$32.59	$32.60	$32.60
7 purchase totals =	$732.56		$809.5869	$809.59	$809.60	$809.60