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	$54.47	7.408%	$58.5051	$58.51	$58.50	$58.50
Purchase #2	$145.59	8.519%	$157.9928	$157.99	$158.00	$158.00
Purchase #3	$79.37	12.599%	$89.3698	$89.37	$89.35	$89.40
Purchase #4	$65.54	11.274%	$72.929	$72.93	$72.95	$72.90
Purchase #5	$101.62	7.498%	$109.2395	$109.24	$109.25	$109.20
Purchase #6	$163.58	10.328%	$180.4745	$180.47	$180.45	$180.50
Purchase #7	$35.91	7.438%	$38.581	$38.58	$38.60	$38.60
7 purchase totals =	$646.08		$707.0917	$707.09	$707.10	$707.10