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	$6.40	13.613%	$7.2712	$7.27	$7.25	$7.30
Purchase #2	$218.85	5.485%	$230.8539	$230.85	$230.85	$230.90
Purchase #3	$186.56	3.215%	$192.5579	$192.56	$192.55	$192.60
Purchase #4	$126.71	5.234%	$133.342	$133.34	$133.35	$133.30
Purchase #5	$132.49	10.171%	$145.9656	$145.97	$145.95	$146.00
Purchase #6	$160.51	11.820%	$179.4823	$179.48	$179.50	$179.50
Purchase #7	$98.89	4.478%	$103.3183	$103.32	$103.30	$103.30
7 purchase totals =	$930.41		$992.7912	$992.79	$992.75	$992.90