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	$134.75	9.693%	$147.8113	$147.81	$147.80	$147.80
Purchase #2	$202.37	10.213%	$223.038	$223.04	$223.05	$223.00
Purchase #3	$105.30	5.475%	$111.0652	$111.07	$111.05	$111.10
Purchase #4	$22.60	3.389%	$23.3659	$23.37	$23.35	$23.40
Purchase #5	$128.82	13.665%	$146.4233	$146.42	$146.40	$146.40
Purchase #6	$184.34	3.560%	$190.9025	$190.90	$190.90	$190.90
Purchase #7	$123.76	6.146%	$131.3663	$131.37	$131.35	$131.40
7 purchase totals =	$901.94		$973.9725	$973.98	$973.90	$974.00