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	$168.66	6.840%	$180.1963	$180.20	$180.20	$180.20
Purchase #2	$10.54	12.562%	$11.864	$11.86	$11.85	$11.90
Purchase #3	$34.66	7.257%	$37.1753	$37.18	$37.20	$37.20
Purchase #4	$160.32	5.240%	$168.7208	$168.72	$168.70	$168.70
Purchase #5	$239.87	7.804%	$258.5895	$258.59	$258.60	$258.60
Purchase #6	$151.41	11.480%	$168.7919	$168.79	$168.80	$168.80
Purchase #7	$237.75	10.866%	$263.5839	$263.58	$263.60	$263.60
7 purchase totals =	$1,003.21		$1,088.9217	$1,088.92	$1,088.95	$1,089.00