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	$119.92	5.657%	$126.7039	$126.70	$126.70	$126.70
Purchase #2	$112.39	10.220%	$123.8763	$123.88	$123.90	$123.90
Purchase #3	$91.99	9.765%	$100.9728	$100.97	$100.95	$101.00
Purchase #4	$91.32	13.749%	$103.8756	$103.88	$103.90	$103.90
Purchase #5	$32.38	8.512%	$35.1362	$35.14	$35.15	$35.10
Purchase #6	$66.81	11.470%	$74.4731	$74.47	$74.45	$74.50
Purchase #7	$99.57	6.180%	$105.7234	$105.72	$105.70	$105.70
7 purchase totals =	$614.38		$670.7613	$670.76	$670.75	$670.80