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	$124.82	10.486%	$137.9086	$137.91	$137.90	$137.90
Purchase #2	$100.71	9.604%	$110.3822	$110.38	$110.40	$110.40
Purchase #3	$19.73	5.502%	$20.8155	$20.82	$20.80	$20.80
Purchase #4	$185.95	10.362%	$205.2181	$205.22	$205.20	$205.20
Purchase #5	$86.60	4.145%	$90.1896	$90.19	$90.20	$90.20
Purchase #6	$163.90	5.593%	$173.0669	$173.07	$173.05	$173.10
Purchase #7	$219.35	4.267%	$228.7097	$228.71	$228.70	$228.70
7 purchase totals =	$901.06		$966.2906	$966.30	$966.25	$966.30