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	$89.85	13.420%	$101.9079	$101.91	$101.90	$101.90
Purchase #2	$165.86	6.596%	$176.8001	$176.80	$176.80	$176.80
Purchase #3	$73.59	12.504%	$82.7917	$82.79	$82.80	$82.80
Purchase #4	$91.30	4.457%	$95.3692	$95.37	$95.35	$95.40
Purchase #5	$148.48	8.806%	$161.5551	$161.56	$161.55	$161.60
Purchase #6	$13.77	11.868%	$15.4042	$15.40	$15.40	$15.40
Purchase #7	$52.90	3.429%	$54.7139	$54.71	$54.70	$54.70
7 purchase totals =	$635.75		$688.5421	$688.54	$688.50	$688.60