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	$204.73	7.457%	$219.9967	$220.00	$220.00	$220.00
Purchase #2	$241.77	5.234%	$254.4242	$254.42	$254.40	$254.40
Purchase #3	$127.77	7.696%	$137.6032	$137.60	$137.60	$137.60
Purchase #4	$55.75	8.144%	$60.2903	$60.29	$60.30	$60.30
Purchase #5	$188.40	4.186%	$196.2864	$196.29	$196.30	$196.30
Purchase #6	$146.76	10.449%	$162.095	$162.10	$162.10	$162.10
Purchase #7	$36.71	7.808%	$39.5763	$39.58	$39.60	$39.60
7 purchase totals =	$1,001.89		$1,070.2721	$1,070.28	$1,070.30	$1,070.30