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	$204.58	12.680%	$230.5207	$230.52	$230.50	$230.50
Purchase #2	$39.88	7.713%	$42.9559	$42.96	$42.95	$43.00
Purchase #3	$235.49	5.123%	$247.5542	$247.55	$247.55	$247.60
Purchase #4	$133.37	10.613%	$147.5246	$147.52	$147.50	$147.50
Purchase #5	$210.65	4.383%	$219.8828	$219.88	$219.90	$219.90
Purchase #6	$93.31	11.553%	$104.0901	$104.09	$104.10	$104.10
Purchase #7	$92.38	9.279%	$100.9519	$100.95	$100.95	$101.00
7 purchase totals =	$1,009.66		$1,093.4802	$1,093.47	$1,093.45	$1,093.60