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	$6.76	4.588%	$7.0701	$7.07	$7.05	$7.10
Purchase #2	$176.35	12.362%	$198.1504	$198.15	$198.15	$198.20
Purchase #3	$85.41	11.779%	$95.4704	$95.47	$95.45	$95.50
Purchase #4	$127.66	11.431%	$142.2528	$142.25	$142.25	$142.30
Purchase #5	$57.67	13.837%	$65.6498	$65.65	$65.65	$65.60
Purchase #6	$249.75	12.855%	$281.8554	$281.86	$281.85	$281.90
Purchase #7	$215.67	13.500%	$244.7855	$244.79	$244.80	$244.80
7 purchase totals =	$919.27		$1,035.2344	$1,035.24	$1,035.20	$1,035.40