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	$45.46	13.746%	$51.7089	$51.71	$51.70	$51.70
Purchase #2	$48.92	5.277%	$51.5015	$51.50	$51.50	$51.50
Purchase #3	$127.95	8.119%	$138.3383	$138.34	$138.35	$138.30
Purchase #4	$204.29	12.413%	$229.6485	$229.65	$229.65	$229.60
Purchase #5	$188.54	11.667%	$210.537	$210.54	$210.55	$210.50
Purchase #6	$172.53	11.182%	$191.8223	$191.82	$191.80	$191.80
Purchase #7	$129.64	12.297%	$145.5818	$145.58	$145.60	$145.60
7 purchase totals =	$917.33		$1,019.1383	$1,019.14	$1,019.15	$1,019.00