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	$52.99	6.388%	$56.375	$56.38	$56.40	$56.40
Purchase #2	$180.89	5.676%	$191.1573	$191.16	$191.15	$191.20
Purchase #3	$52.54	12.710%	$59.2178	$59.22	$59.20	$59.20
Purchase #4	$172.85	8.172%	$186.9753	$186.98	$187.00	$187.00
Purchase #5	$98.31	13.296%	$111.3813	$111.38	$111.40	$111.40
Purchase #6	$112.50	4.502%	$117.5648	$117.56	$117.55	$117.60
Purchase #7	$48.68	10.263%	$53.676	$53.68	$53.70	$53.70
7 purchase totals =	$718.76		$776.3475	$776.36	$776.40	$776.50