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	$241.55	8.307%	$261.6156	$261.62	$261.60	$261.60
Purchase #2	$171.61	9.251%	$187.4856	$187.49	$187.50	$187.50
Purchase #3	$128.35	12.319%	$144.1614	$144.16	$144.15	$144.20
Purchase #4	$167.76	3.424%	$173.5041	$173.50	$173.50	$173.50
Purchase #5	$233.85	9.164%	$255.28	$255.28	$255.30	$255.30
Purchase #6	$143.46	7.288%	$153.9154	$153.92	$153.90	$153.90
Purchase #7	$95.91	6.688%	$102.3245	$102.32	$102.30	$102.30
7 purchase totals =	$1,182.49		$1,278.2866	$1,278.29	$1,278.25	$1,278.30