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	$213.99	3.646%	$221.7921	$221.79	$221.80	$221.80
Purchase #2	$211.38	5.298%	$222.5789	$222.58	$222.60	$222.60
Purchase #3	$16.80	7.792%	$18.1091	$18.11	$18.10	$18.10
Purchase #4	$228.45	12.157%	$256.2227	$256.22	$256.20	$256.20
Purchase #5	$221.59	12.346%	$248.9475	$248.95	$248.95	$248.90
Purchase #6	$136.63	7.181%	$146.4414	$146.44	$146.45	$146.40
Purchase #7	$52.38	10.629%	$57.9475	$57.95	$57.95	$57.90
7 purchase totals =	$1,081.22		$1,172.0392	$1,172.04	$1,172.05	$1,171.90