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	$26.81	10.728%	$29.6862	$29.69	$29.70	$29.70
Purchase #2	$231.34	8.205%	$250.3214	$250.32	$250.30	$250.30
Purchase #3	$51.64	10.751%	$57.1918	$57.19	$57.20	$57.20
Purchase #4	$98.32	6.478%	$104.6892	$104.69	$104.70	$104.70
Purchase #5	$98.38	13.665%	$111.8236	$111.82	$111.80	$111.80
Purchase #6	$220.32	4.829%	$230.9593	$230.96	$230.95	$231.00
Purchase #7	$244.79	3.592%	$253.5829	$253.58	$253.60	$253.60
7 purchase totals =	$971.60		$1,038.2544	$1,038.25	$1,038.25	$1,038.30