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	$219.62	12.847%	$247.8346	$247.83	$247.85	$247.80
Purchase #2	$79.46	13.390%	$90.0997	$90.10	$90.10	$90.10
Purchase #3	$191.42	13.856%	$217.9432	$217.94	$217.95	$217.90
Purchase #4	$27.50	13.316%	$31.1619	$31.16	$31.15	$31.20
Purchase #5	$228.33	10.562%	$252.4462	$252.45	$252.45	$252.40
Purchase #6	$125.96	13.819%	$143.3664	$143.37	$143.35	$143.40
Purchase #7	$35.29	7.707%	$38.0098	$38.01	$38.00	$38.00
7 purchase totals =	$907.58		$1,020.8618	$1,020.86	$1,020.85	$1,020.80