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	$94.67	5.182%	$99.5758	$99.58	$99.60	$99.60
Purchase #2	$207.30	13.806%	$235.9198	$235.92	$235.90	$235.90
Purchase #3	$99.72	3.421%	$103.1314	$103.13	$103.15	$103.10
Purchase #4	$216.46	5.466%	$228.2917	$228.29	$228.30	$228.30
Purchase #5	$228.48	4.289%	$238.2795	$238.28	$238.30	$238.30
Purchase #6	$248.57	4.447%	$259.6239	$259.62	$259.60	$259.60
Purchase #7	$227.61	12.234%	$255.4558	$255.46	$255.45	$255.50
7 purchase totals =	$1,322.81		$1,420.2779	$1,420.28	$1,420.30	$1,420.30