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	$222.89	13.337%	$252.6168	$252.62	$252.60	$252.60
Purchase #2	$41.30	3.674%	$42.8174	$42.82	$42.80	$42.80
Purchase #3	$205.40	8.703%	$223.276	$223.28	$223.30	$223.30
Purchase #4	$31.89	12.341%	$35.8255	$35.83	$35.85	$35.80
Purchase #5	$31.67	4.343%	$33.0454	$33.05	$33.05	$33.00
Purchase #6	$88.52	10.253%	$97.596	$97.60	$97.60	$97.60
Purchase #7	$136.64	7.479%	$146.8593	$146.86	$146.85	$146.90
7 purchase totals =	$758.31		$832.0364	$832.06	$832.05	$832.00