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	$90.49	8.722%	$98.3825	$98.38	$98.40	$98.40
Purchase #2	$19.81	13.409%	$22.4663	$22.47	$22.45	$22.50
Purchase #3	$217.34	7.253%	$233.1037	$233.10	$233.10	$233.10
Purchase #4	$50.61	7.238%	$54.2732	$54.27	$54.25	$54.30
Purchase #5	$205.68	8.842%	$223.8662	$223.87	$223.85	$223.90
Purchase #6	$109.47	9.253%	$119.5993	$119.60	$119.60	$119.60
Purchase #7	$136.60	9.425%	$149.4746	$149.47	$149.45	$149.50
7 purchase totals =	$830.00		$901.1658	$901.16	$901.10	$901.30