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	$197.42	12.581%	$222.2574	$222.26	$222.25	$222.30
Purchase #2	$84.91	9.597%	$93.0588	$93.06	$93.05	$93.10
Purchase #3	$107.81	13.484%	$122.3471	$122.35	$122.35	$122.30
Purchase #4	$53.45	11.506%	$59.6	$59.60	$59.60	$59.60
Purchase #5	$103.75	7.597%	$111.6319	$111.63	$111.65	$111.60
Purchase #6	$151.78	4.415%	$158.4811	$158.48	$158.50	$158.50
Purchase #7	$204.53	10.648%	$226.3084	$226.31	$226.30	$226.30
7 purchase totals =	$903.65		$993.6847	$993.69	$993.70	$993.70