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	$14.37	6.324%	$15.2788	$15.28	$15.30	$15.30
Purchase #2	$69.43	12.279%	$77.9553	$77.96	$77.95	$78.00
Purchase #3	$103.50	7.345%	$111.1021	$111.10	$111.10	$111.10
Purchase #4	$112.42	9.203%	$122.766	$122.77	$122.75	$122.80
Purchase #5	$250.52	4.751%	$262.4222	$262.42	$262.40	$262.40
Purchase #6	$120.83	8.747%	$131.399	$131.40	$131.40	$131.40
Purchase #7	$168.29	6.593%	$179.3854	$179.39	$179.40	$179.40
7 purchase totals =	$839.36		$900.3088	$900.32	$900.30	$900.40