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	$207.94	6.511%	$221.479	$221.48	$221.50	$221.50
Purchase #2	$198.32	6.689%	$211.5856	$211.59	$211.60	$211.60
Purchase #3	$49.39	5.356%	$52.0353	$52.04	$52.05	$52.00
Purchase #4	$48.30	8.198%	$52.2596	$52.26	$52.25	$52.30
Purchase #5	$74.70	10.412%	$82.4778	$82.48	$82.50	$82.50
Purchase #6	$104.42	9.361%	$114.1948	$114.19	$114.20	$114.20
Purchase #7	$127.91	7.581%	$137.6069	$137.61	$137.60	$137.60
7 purchase totals =	$810.98		$871.6390	$871.65	$871.70	$871.70