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	$97.72	13.744%	$111.1506	$111.15	$111.15	$111.20
Purchase #2	$245.43	8.284%	$265.7614	$265.76	$265.75	$265.80
Purchase #3	$166.98	11.547%	$186.2612	$186.26	$186.25	$186.30
Purchase #4	$237.45	7.764%	$255.8856	$255.89	$255.90	$255.90
Purchase #5	$96.29	7.327%	$103.3452	$103.35	$103.35	$103.30
Purchase #6	$58.91	4.420%	$61.5138	$61.51	$61.50	$61.50
Purchase #7	$173.60	8.439%	$188.2501	$188.25	$188.25	$188.30
7 purchase totals =	$1,076.38		$1,172.1679	$1,172.17	$1,172.15	$1,172.30