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	$49.51	3.357%	$51.1721	$51.17	$51.15	$51.20
Purchase #2	$92.87	9.426%	$101.6239	$101.62	$101.60	$101.60
Purchase #3	$95.72	4.172%	$99.7134	$99.71	$99.70	$99.70
Purchase #4	$119.67	9.285%	$130.7814	$130.78	$130.80	$130.80
Purchase #5	$7.92	12.241%	$8.8895	$8.89	$8.90	$8.90
Purchase #6	$109.56	6.488%	$116.6683	$116.67	$116.65	$116.70
Purchase #7	$250.30	8.849%	$272.449	$272.45	$272.45	$272.40
7 purchase totals =	$725.55		$781.2976	$781.29	$781.25	$781.30