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	$239.62	8.203%	$259.276	$259.28	$259.30	$259.30
Purchase #2	$174.84	12.284%	$196.3173	$196.32	$196.30	$196.30
Purchase #3	$194.72	10.495%	$215.1559	$215.16	$215.15	$215.20
Purchase #4	$154.56	9.281%	$168.9047	$168.90	$168.90	$168.90
Purchase #5	$203.97	5.377%	$214.9375	$214.94	$214.95	$214.90
Purchase #6	$136.94	11.161%	$152.2239	$152.22	$152.20	$152.20
Purchase #7	$17.92	3.685%	$18.5804	$18.58	$18.60	$18.60
7 purchase totals =	$1,122.57		$1,225.3957	$1,225.40	$1,225.40	$1,225.40