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	$19.43	3.753%	$20.1592	$20.16	$20.15	$20.20
Purchase #2	$171.63	13.259%	$194.3864	$194.39	$194.40	$194.40
Purchase #3	$90.59	12.451%	$101.8694	$101.87	$101.85	$101.90
Purchase #4	$129.59	12.409%	$145.6708	$145.67	$145.65	$145.70
Purchase #5	$99.97	13.713%	$113.6789	$113.68	$113.70	$113.70
Purchase #6	$59.88	9.169%	$65.3704	$65.37	$65.35	$65.40
Purchase #7	$48.89	7.287%	$52.4526	$52.45	$52.45	$52.50
7 purchase totals =	$619.98		$693.5877	$693.59	$693.55	$693.80