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	$143.36	5.600%	$151.3882	$151.39	$151.40	$151.40
Purchase #2	$127.27	13.608%	$144.5889	$144.59	$144.60	$144.60
Purchase #3	$249.83	13.280%	$283.0074	$283.01	$283.00	$283.00
Purchase #4	$69.73	10.383%	$76.9701	$76.97	$76.95	$77.00
Purchase #5	$147.29	12.135%	$165.1636	$165.16	$165.15	$165.20
Purchase #6	$101.52	9.732%	$111.3999	$111.40	$111.40	$111.40
Purchase #7	$142.36	3.129%	$146.8144	$146.81	$146.80	$146.80
7 purchase totals =	$981.36		$1,079.3325	$1,079.33	$1,079.30	$1,079.40