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	$159.29	7.675%	$171.5155	$171.52	$171.50	$171.50
Purchase #2	$124.32	3.707%	$128.9285	$128.93	$128.95	$128.90
Purchase #3	$36.43	13.145%	$41.2187	$41.22	$41.20	$41.20
Purchase #4	$95.54	7.480%	$102.6864	$102.69	$102.70	$102.70
Purchase #5	$224.54	6.197%	$238.4547	$238.45	$238.45	$238.50
Purchase #6	$205.71	4.295%	$214.5452	$214.55	$214.55	$214.50
Purchase #7	$175.44	9.104%	$191.4121	$191.41	$191.40	$191.40
7 purchase totals =	$1,021.27		$1,088.7611	$1,088.77	$1,088.75	$1,088.70