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	$245.93	13.580%	$279.3273	$279.33	$279.35	$279.30
Purchase #2	$39.51	5.753%	$41.783	$41.78	$41.80	$41.80
Purchase #3	$58.30	6.527%	$62.1052	$62.11	$62.10	$62.10
Purchase #4	$12.68	11.817%	$14.1784	$14.18	$14.20	$14.20
Purchase #5	$65.31	10.578%	$72.2185	$72.22	$72.20	$72.20
Purchase #6	$116.53	4.258%	$121.4918	$121.49	$121.50	$121.50
Purchase #7	$90.34	10.313%	$99.6568	$99.66	$99.65	$99.70
7 purchase totals =	$628.60		$690.7610	$690.77	$690.80	$690.80