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	$99.88	11.618%	$111.4841	$111.48	$111.50	$111.50
Purchase #2	$91.33	10.830%	$101.221	$101.22	$101.20	$101.20
Purchase #3	$248.68	9.624%	$272.613	$272.61	$272.60	$272.60
Purchase #4	$92.37	9.824%	$101.4444	$101.44	$101.45	$101.40
Purchase #5	$173.72	9.729%	$190.6212	$190.62	$190.60	$190.60
Purchase #6	$47.93	4.452%	$50.0638	$50.06	$50.05	$50.10
Purchase #7	$19.49	4.442%	$20.3557	$20.36	$20.35	$20.40
7 purchase totals =	$773.40		$847.8032	$847.79	$847.75	$847.80