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	$177.58	12.847%	$200.3937	$200.39	$200.40	$200.40
Purchase #2	$99.29	10.546%	$109.7611	$109.76	$109.75	$109.80
Purchase #3	$39.40	3.499%	$40.7786	$40.78	$40.80	$40.80
Purchase #4	$132.77	13.434%	$150.6063	$150.61	$150.60	$150.60
Purchase #5	$148.65	4.665%	$155.5845	$155.58	$155.60	$155.60
Purchase #6	$67.75	9.638%	$74.2797	$74.28	$74.30	$74.30
Purchase #7	$221.32	9.235%	$241.7589	$241.76	$241.75	$241.80
7 purchase totals =	$886.76		$973.1628	$973.16	$973.20	$973.30