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	$159.86	12.768%	$180.2709	$180.27	$180.25	$180.30
Purchase #2	$235.99	7.656%	$254.0574	$254.06	$254.05	$254.10
Purchase #3	$187.93	4.447%	$196.2872	$196.29	$196.30	$196.30
Purchase #4	$188.90	13.866%	$215.0929	$215.09	$215.10	$215.10
Purchase #5	$242.76	5.170%	$255.3107	$255.31	$255.30	$255.30
Purchase #6	$38.28	8.261%	$41.4423	$41.44	$41.45	$41.40
Purchase #7	$144.38	12.354%	$162.2167	$162.22	$162.20	$162.20
7 purchase totals =	$1,198.10		$1,304.6781	$1,304.68	$1,304.65	$1,304.70