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	$152.65	4.354%	$159.2964	$159.30	$159.30	$159.30
Purchase #2	$203.72	10.784%	$225.6892	$225.69	$225.70	$225.70
Purchase #3	$135.65	7.262%	$145.5009	$145.50	$145.50	$145.50
Purchase #4	$36.47	8.311%	$39.501	$39.50	$39.50	$39.50
Purchase #5	$180.98	3.841%	$187.9314	$187.93	$187.95	$187.90
Purchase #6	$107.94	5.433%	$113.8044	$113.80	$113.80	$113.80
Purchase #7	$160.87	4.792%	$168.5789	$168.58	$168.60	$168.60
7 purchase totals =	$978.28		$1,040.3022	$1,040.30	$1,040.35	$1,040.30