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	$226.72	13.161%	$256.5586	$256.56	$256.55	$256.60
Purchase #2	$11.32	11.375%	$12.6077	$12.61	$12.60	$12.60
Purchase #3	$121.59	8.809%	$132.3009	$132.30	$132.30	$132.30
Purchase #4	$142.55	5.648%	$150.6012	$150.60	$150.60	$150.60
Purchase #5	$108.85	11.623%	$121.5016	$121.50	$121.50	$121.50
Purchase #6	$136.74	11.614%	$152.621	$152.62	$152.60	$152.60
Purchase #7	$136.48	5.847%	$144.46	$144.46	$144.45	$144.50
7 purchase totals =	$884.25		$970.6510	$970.65	$970.60	$970.70