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	$167.46	4.403%	$174.8333	$174.83	$174.85	$174.80
Purchase #2	$114.98	7.646%	$123.7714	$123.77	$123.75	$123.80
Purchase #3	$132.36	3.826%	$137.4241	$137.42	$137.40	$137.40
Purchase #4	$34.51	11.414%	$38.449	$38.45	$38.45	$38.40
Purchase #5	$173.65	6.658%	$185.2116	$185.21	$185.20	$185.20
Purchase #6	$66.60	3.492%	$68.9257	$68.93	$68.95	$68.90
Purchase #7	$114.44	11.450%	$127.5434	$127.54	$127.55	$127.50
7 purchase totals =	$804.00		$856.1585	$856.15	$856.15	$856.00