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	$247.34	11.846%	$276.6399	$276.64	$276.65	$276.60
Purchase #2	$127.91	6.554%	$136.2932	$136.29	$136.30	$136.30
Purchase #3	$57.33	3.108%	$59.1118	$59.11	$59.10	$59.10
Purchase #4	$224.58	3.842%	$233.2084	$233.21	$233.20	$233.20
Purchase #5	$106.35	7.707%	$114.5464	$114.55	$114.55	$114.50
Purchase #6	$122.86	3.431%	$127.0753	$127.08	$127.10	$127.10
Purchase #7	$30.78	10.225%	$33.9273	$33.93	$33.95	$33.90
7 purchase totals =	$917.15		$980.8023	$980.81	$980.85	$980.70