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	$105.67	6.262%	$112.2871	$112.29	$112.30	$112.30
Purchase #2	$129.83	8.834%	$141.2992	$141.30	$141.30	$141.30
Purchase #3	$240.39	6.659%	$256.3976	$256.40	$256.40	$256.40
Purchase #4	$239.70	10.235%	$264.2333	$264.23	$264.25	$264.20
Purchase #5	$66.95	4.529%	$69.9822	$69.98	$70.00	$70.00
Purchase #6	$100.31	5.424%	$105.7508	$105.75	$105.75	$105.80
Purchase #7	$174.25	9.197%	$190.2758	$190.28	$190.30	$190.30
7 purchase totals =	$1,057.10		$1,140.2260	$1,140.23	$1,140.30	$1,140.30