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	$115.37	12.737%	$130.0647	$130.06	$130.05	$130.10
Purchase #2	$131.50	11.530%	$146.662	$146.66	$146.65	$146.70
Purchase #3	$151.51	3.636%	$157.0189	$157.02	$157.00	$157.00
Purchase #4	$37.51	4.209%	$39.0888	$39.09	$39.10	$39.10
Purchase #5	$101.59	11.117%	$112.8838	$112.88	$112.90	$112.90
Purchase #6	$146.76	13.450%	$166.4992	$166.50	$166.50	$166.50
Purchase #7	$96.53	6.718%	$103.0149	$103.01	$103.00	$103.00
7 purchase totals =	$780.77		$855.2323	$855.22	$855.20	$855.30