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	$98.99	6.190%	$105.1175	$105.12	$105.10	$105.10
Purchase #2	$76.69	7.519%	$82.4563	$82.46	$82.45	$82.50
Purchase #3	$42.90	13.308%	$48.6091	$48.61	$48.60	$48.60
Purchase #4	$38.50	4.275%	$40.1459	$40.15	$40.15	$40.10
Purchase #5	$213.81	13.356%	$242.3665	$242.37	$242.35	$242.40
Purchase #6	$151.52	12.749%	$170.8373	$170.84	$170.85	$170.80
Purchase #7	$83.42	3.319%	$86.1887	$86.19	$86.20	$86.20
7 purchase totals =	$705.83		$775.7213	$775.74	$775.70	$775.70