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	$180.89	5.787%	$191.3581	$191.36	$191.35	$191.40
Purchase #2	$17.82	13.142%	$20.1619	$20.16	$20.15	$20.20
Purchase #3	$190.98	13.671%	$217.0889	$217.09	$217.10	$217.10
Purchase #4	$248.84	12.468%	$279.8654	$279.87	$279.85	$279.90
Purchase #5	$245.94	8.302%	$266.3579	$266.36	$266.35	$266.40
Purchase #6	$160.39	12.385%	$180.2543	$180.25	$180.25	$180.30
Purchase #7	$36.84	13.485%	$41.8079	$41.81	$41.80	$41.80
7 purchase totals =	$1,081.70		$1,196.8944	$1,196.90	$1,196.85	$1,197.10