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	$121.66	9.514%	$133.2347	$133.23	$133.25	$133.20
Purchase #2	$6.40	11.592%	$7.1419	$7.14	$7.15	$7.10
Purchase #3	$66.46	6.157%	$70.5519	$70.55	$70.55	$70.60
Purchase #4	$148.37	4.561%	$155.1372	$155.14	$155.15	$155.10
Purchase #5	$96.28	7.528%	$103.528	$103.53	$103.55	$103.50
Purchase #6	$37.64	5.152%	$39.5792	$39.58	$39.60	$39.60
Purchase #7	$186.77	7.153%	$200.1297	$200.13	$200.15	$200.10
7 purchase totals =	$663.58		$709.3026	$709.30	$709.40	$709.20