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	$49.67	7.303%	$53.2974	$53.30	$53.30	$53.30
Purchase #2	$93.82	11.146%	$104.2772	$104.28	$104.30	$104.30
Purchase #3	$94.29	10.166%	$103.8755	$103.88	$103.90	$103.90
Purchase #4	$45.80	5.566%	$48.3492	$48.35	$48.35	$48.30
Purchase #5	$95.26	4.696%	$99.7334	$99.73	$99.75	$99.70
Purchase #6	$128.58	6.595%	$137.0599	$137.06	$137.05	$137.10
Purchase #7	$123.35	8.450%	$133.7731	$133.77	$133.75	$133.80
7 purchase totals =	$630.77		$680.3657	$680.37	$680.40	$680.40