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	$240.46	13.294%	$272.4268	$272.43	$272.45	$272.40
Purchase #2	$57.60	13.603%	$65.4353	$65.44	$65.45	$65.40
Purchase #3	$103.82	7.426%	$111.5297	$111.53	$111.55	$111.50
Purchase #4	$83.53	6.170%	$88.6838	$88.68	$88.70	$88.70
Purchase #5	$187.79	5.447%	$198.0189	$198.02	$198.00	$198.00
Purchase #6	$88.52	3.670%	$91.7687	$91.77	$91.75	$91.80
Purchase #7	$97.70	6.507%	$104.0573	$104.06	$104.05	$104.10
7 purchase totals =	$859.42		$931.9205	$931.93	$931.95	$931.90