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	$30.43	7.489%	$32.7089	$32.71	$32.70	$32.70
Purchase #2	$75.64	9.162%	$82.5701	$82.57	$82.55	$82.60
Purchase #3	$109.41	5.543%	$115.4746	$115.47	$115.45	$115.50
Purchase #4	$136.94	13.404%	$155.2954	$155.30	$155.30	$155.30
Purchase #5	$111.53	6.242%	$118.4917	$118.49	$118.50	$118.50
Purchase #6	$50.35	10.479%	$55.6262	$55.63	$55.65	$55.60
Purchase #7	$20.72	3.870%	$21.5219	$21.52	$21.50	$21.50
7 purchase totals =	$535.02		$581.6888	$581.69	$581.65	$581.70