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	$100.55	10.615%	$111.2234	$111.22	$111.20	$111.20
Purchase #2	$59.82	3.712%	$62.0405	$62.04	$62.05	$62.00
Purchase #3	$249.36	7.323%	$267.6206	$267.62	$267.60	$267.60
Purchase #4	$35.89	7.359%	$38.5311	$38.53	$38.55	$38.50
Purchase #5	$70.47	13.503%	$79.9856	$79.99	$80.00	$80.00
Purchase #6	$109.27	7.607%	$117.5822	$117.58	$117.60	$117.60
Purchase #7	$96.52	9.449%	$105.6402	$105.64	$105.65	$105.60
7 purchase totals =	$721.88		$782.6236	$782.62	$782.65	$782.50