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	$24.50	9.728%	$26.8834	$26.88	$26.90	$26.90
Purchase #2	$87.40	3.152%	$90.1548	$90.15	$90.15	$90.20
Purchase #3	$14.73	5.325%	$15.5144	$15.51	$15.50	$15.50
Purchase #4	$75.98	7.126%	$81.3943	$81.39	$81.40	$81.40
Purchase #5	$202.87	7.736%	$218.564	$218.56	$218.55	$218.60
Purchase #6	$151.91	13.688%	$172.7034	$172.70	$172.70	$172.70
Purchase #7	$85.40	5.345%	$89.9646	$89.96	$89.95	$90.00
7 purchase totals =	$642.79		$695.1789	$695.15	$695.15	$695.30