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	$91.64	9.612%	$100.4484	$100.45	$100.45	$100.40
Purchase #2	$188.60	9.499%	$206.5151	$206.52	$206.50	$206.50
Purchase #3	$136.95	8.564%	$148.6784	$148.68	$148.70	$148.70
Purchase #4	$188.53	4.260%	$196.5614	$196.56	$196.55	$196.60
Purchase #5	$21.64	10.448%	$23.9009	$23.90	$23.90	$23.90
Purchase #6	$91.37	10.228%	$100.7153	$100.72	$100.70	$100.70
Purchase #7	$118.94	4.526%	$124.3232	$124.32	$124.30	$124.30
7 purchase totals =	$837.67		$901.1427	$901.15	$901.10	$901.10