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	$72.80	7.732%	$78.4289	$78.43	$78.45	$78.40
Purchase #2	$134.62	11.739%	$150.423	$150.42	$150.40	$150.40
Purchase #3	$49.49	5.728%	$52.3248	$52.32	$52.30	$52.30
Purchase #4	$212.39	7.719%	$228.7844	$228.78	$228.80	$228.80
Purchase #5	$160.55	11.813%	$179.5158	$179.52	$179.50	$179.50
Purchase #6	$122.33	5.275%	$128.7829	$128.78	$128.80	$128.80
Purchase #7	$248.93	12.152%	$279.18	$279.18	$279.20	$279.20
7 purchase totals =	$1,001.11		$1,097.4398	$1,097.43	$1,097.45	$1,097.40