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	$157.90	13.653%	$179.4581	$179.46	$179.45	$179.50
Purchase #2	$158.85	9.254%	$173.55	$173.55	$173.55	$173.60
Purchase #3	$99.57	10.276%	$109.8018	$109.80	$109.80	$109.80
Purchase #4	$191.74	5.836%	$202.9299	$202.93	$202.95	$202.90
Purchase #5	$48.91	11.150%	$54.3635	$54.36	$54.35	$54.40
Purchase #6	$6.37	7.510%	$6.8484	$6.85	$6.85	$6.80
Purchase #7	$250.25	6.536%	$266.6063	$266.61	$266.60	$266.60
7 purchase totals =	$913.59		$993.5580	$993.56	$993.55	$993.60