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	$61.42	6.138%	$65.19	$65.19	$65.20	$65.20
Purchase #2	$124.44	12.146%	$139.5545	$139.55	$139.55	$139.60
Purchase #3	$185.66	5.777%	$196.3856	$196.39	$196.40	$196.40
Purchase #4	$166.87	6.807%	$178.2288	$178.23	$178.25	$178.20
Purchase #5	$101.60	10.823%	$112.5962	$112.60	$112.60	$112.60
Purchase #6	$49.54	9.815%	$54.4024	$54.40	$54.40	$54.40
Purchase #7	$58.67	7.654%	$63.1606	$63.16	$63.15	$63.20
7 purchase totals =	$748.20		$809.5181	$809.52	$809.55	$809.60