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	$91.72	12.389%	$103.0832	$103.08	$103.10	$103.10
Purchase #2	$224.52	5.788%	$237.5152	$237.52	$237.50	$237.50
Purchase #3	$20.86	4.169%	$21.7297	$21.73	$21.75	$21.70
Purchase #4	$87.72	8.820%	$95.4569	$95.46	$95.45	$95.50
Purchase #5	$162.78	11.342%	$181.2425	$181.24	$181.25	$181.20
Purchase #6	$150.27	5.529%	$158.5784	$158.58	$158.60	$158.60
Purchase #7	$55.58	3.458%	$57.502	$57.50	$57.50	$57.50
7 purchase totals =	$793.45		$855.1079	$855.11	$855.15	$855.10