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	$83.91	8.561%	$91.0935	$91.09	$91.10	$91.10
Purchase #2	$196.58	10.420%	$217.0636	$217.06	$217.05	$217.10
Purchase #3	$119.30	10.863%	$132.2596	$132.26	$132.25	$132.30
Purchase #4	$55.32	7.293%	$59.3545	$59.35	$59.35	$59.40
Purchase #5	$178.52	3.362%	$184.5218	$184.52	$184.50	$184.50
Purchase #6	$217.91	5.329%	$229.5224	$229.52	$229.50	$229.50
Purchase #7	$76.68	4.551%	$80.1697	$80.17	$80.15	$80.20
7 purchase totals =	$928.22		$993.9851	$993.97	$993.90	$994.10