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	$141.85	12.527%	$159.6195	$159.62	$159.60	$159.60
Purchase #2	$106.67	3.777%	$110.6989	$110.70	$110.70	$110.70
Purchase #3	$38.32	11.112%	$42.5781	$42.58	$42.60	$42.60
Purchase #4	$118.34	13.646%	$134.4887	$134.49	$134.50	$134.50
Purchase #5	$139.45	9.545%	$152.7605	$152.76	$152.75	$152.80
Purchase #6	$240.54	10.315%	$265.3517	$265.35	$265.35	$265.40
Purchase #7	$63.65	5.813%	$67.35	$67.35	$67.35	$67.40
7 purchase totals =	$848.82		$932.8474	$932.85	$932.85	$933.00