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	$40.91	4.223%	$42.6376	$42.64	$42.65	$42.60
Purchase #2	$41.33	3.622%	$42.827	$42.83	$42.85	$42.80
Purchase #3	$102.99	10.766%	$114.0779	$114.08	$114.10	$114.10
Purchase #4	$83.37	9.229%	$91.0642	$91.06	$91.05	$91.10
Purchase #5	$61.52	13.692%	$69.9433	$69.94	$69.95	$69.90
Purchase #6	$184.44	10.228%	$203.3045	$203.30	$203.30	$203.30
Purchase #7	$52.64	12.338%	$59.1347	$59.13	$59.15	$59.10
7 purchase totals =	$567.20		$622.9892	$622.98	$623.05	$622.90