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	$54.91	3.728%	$56.957	$56.96	$56.95	$57.00
Purchase #2	$189.25	6.808%	$202.1341	$202.13	$202.15	$202.10
Purchase #3	$97.85	5.405%	$103.1388	$103.14	$103.15	$103.10
Purchase #4	$58.29	7.420%	$62.6151	$62.62	$62.60	$62.60
Purchase #5	$172.41	7.609%	$185.5287	$185.53	$185.55	$185.50
Purchase #6	$245.69	3.310%	$253.8223	$253.82	$253.80	$253.80
Purchase #7	$66.94	8.152%	$72.3969	$72.40	$72.40	$72.40
7 purchase totals =	$885.34		$936.5929	$936.60	$936.60	$936.50