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	$80.83	6.190%	$85.8334	$85.83	$85.85	$85.80
Purchase #2	$16.99	10.668%	$18.8025	$18.80	$18.80	$18.80
Purchase #3	$190.32	13.372%	$215.7696	$215.77	$215.75	$215.80
Purchase #4	$22.75	7.841%	$24.5338	$24.53	$24.55	$24.50
Purchase #5	$119.25	3.180%	$123.0422	$123.04	$123.05	$123.00
Purchase #6	$145.94	4.596%	$152.6474	$152.65	$152.65	$152.60
Purchase #7	$61.35	6.796%	$65.5193	$65.52	$65.50	$65.50
7 purchase totals =	$637.43		$686.1482	$686.14	$686.15	$686.00