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	$103.59	12.139%	$116.1648	$116.16	$116.15	$116.20
Purchase #2	$225.75	9.754%	$247.7697	$247.77	$247.75	$247.80
Purchase #3	$164.56	4.543%	$172.036	$172.04	$172.05	$172.00
Purchase #4	$113.59	13.866%	$129.3404	$129.34	$129.35	$129.30
Purchase #5	$39.56	4.689%	$41.415	$41.42	$41.40	$41.40
Purchase #6	$136.45	10.604%	$150.9192	$150.92	$150.90	$150.90
Purchase #7	$128.78	11.157%	$143.148	$143.15	$143.15	$143.10
7 purchase totals =	$912.28		$1,000.7931	$1,000.80	$1,000.75	$1,000.70