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	$134.87	11.266%	$150.0645	$150.06	$150.05	$150.10
Purchase #2	$219.52	12.794%	$247.6054	$247.61	$247.60	$247.60
Purchase #3	$107.77	11.461%	$120.1215	$120.12	$120.10	$120.10
Purchase #4	$40.28	13.249%	$45.6167	$45.62	$45.60	$45.60
Purchase #5	$131.97	9.370%	$144.3356	$144.34	$144.35	$144.30
Purchase #6	$245.40	4.534%	$256.5264	$256.53	$256.55	$256.50
Purchase #7	$49.97	6.535%	$53.2355	$53.24	$53.25	$53.20
7 purchase totals =	$929.78		$1,017.5056	$1,017.52	$1,017.50	$1,017.40