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	$47.28	9.185%	$51.6227	$51.62	$51.60	$51.60
Purchase #2	$55.31	13.589%	$62.8261	$62.83	$62.85	$62.80
Purchase #3	$51.67	8.647%	$56.1379	$56.14	$56.15	$56.10
Purchase #4	$210.86	10.548%	$233.1015	$233.10	$233.10	$233.10
Purchase #5	$166.79	7.571%	$179.4177	$179.42	$179.40	$179.40
Purchase #6	$117.40	11.420%	$130.8071	$130.81	$130.80	$130.80
Purchase #7	$61.37	10.647%	$67.9041	$67.90	$67.90	$67.90
7 purchase totals =	$710.68		$781.8171	$781.82	$781.80	$781.70