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	$211.86	4.591%	$221.5865	$221.59	$221.60	$221.60
Purchase #2	$16.75	12.411%	$18.8288	$18.83	$18.85	$18.80
Purchase #3	$101.68	9.207%	$111.0417	$111.04	$111.05	$111.00
Purchase #4	$38.88	7.748%	$41.8924	$41.89	$41.90	$41.90
Purchase #5	$19.86	5.108%	$20.8744	$20.87	$20.85	$20.90
Purchase #6	$142.27	4.576%	$148.7803	$148.78	$148.80	$148.80
Purchase #7	$49.95	7.668%	$53.7802	$53.78	$53.80	$53.80
7 purchase totals =	$581.25		$616.7843	$616.78	$616.85	$616.80