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	$246.37	3.599%	$255.2369	$255.24	$255.25	$255.20
Purchase #2	$219.62	12.560%	$247.2043	$247.20	$247.20	$247.20
Purchase #3	$122.49	7.658%	$131.8703	$131.87	$131.85	$131.90
Purchase #4	$84.40	6.836%	$90.1696	$90.17	$90.15	$90.20
Purchase #5	$85.28	4.104%	$88.7799	$88.78	$88.80	$88.80
Purchase #6	$12.98	3.398%	$13.4211	$13.42	$13.40	$13.40
Purchase #7	$155.30	6.655%	$165.6352	$165.64	$165.65	$165.60
7 purchase totals =	$926.44		$992.3173	$992.32	$992.30	$992.30