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	$244.52	12.588%	$275.3002	$275.30	$275.30	$275.30
Purchase #2	$33.88	9.865%	$37.2223	$37.22	$37.20	$37.20
Purchase #3	$230.82	4.666%	$241.5901	$241.59	$241.60	$241.60
Purchase #4	$98.72	6.541%	$105.1773	$105.18	$105.20	$105.20
Purchase #5	$162.91	5.712%	$172.2154	$172.22	$172.20	$172.20
Purchase #6	$89.62	11.440%	$99.8725	$99.87	$99.85	$99.90
Purchase #7	$55.83	7.106%	$59.7973	$59.80	$59.80	$59.80
7 purchase totals =	$916.30		$991.1751	$991.18	$991.15	$991.20