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	$91.51	10.125%	$100.7754	$100.78	$100.80	$100.80
Purchase #2	$39.64	10.395%	$43.7606	$43.76	$43.75	$43.80
Purchase #3	$86.71	5.451%	$91.4366	$91.44	$91.45	$91.40
Purchase #4	$227.63	7.290%	$244.2242	$244.22	$244.20	$244.20
Purchase #5	$248.89	8.140%	$269.1496	$269.15	$269.15	$269.10
Purchase #6	$172.38	8.245%	$186.5927	$186.59	$186.60	$186.60
Purchase #7	$116.87	7.457%	$125.585	$125.59	$125.60	$125.60
7 purchase totals =	$983.63		$1,061.5241	$1,061.53	$1,061.55	$1,061.50