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	$62.74	12.311%	$70.4639	$70.46	$70.45	$70.50
Purchase #2	$242.93	13.390%	$275.4583	$275.46	$275.45	$275.50
Purchase #3	$132.35	10.495%	$146.2401	$146.24	$146.25	$146.20
Purchase #4	$46.91	10.741%	$51.9486	$51.95	$51.95	$51.90
Purchase #5	$179.50	9.445%	$196.4538	$196.45	$196.45	$196.50
Purchase #6	$242.38	6.128%	$257.233	$257.23	$257.25	$257.20
Purchase #7	$52.72	7.272%	$56.5538	$56.55	$56.55	$56.60
7 purchase totals =	$959.53		$1,054.3515	$1,054.34	$1,054.35	$1,054.40