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	$173.91	13.220%	$196.9009	$196.90	$196.90	$196.90
Purchase #2	$126.40	4.698%	$132.3383	$132.34	$132.35	$132.30
Purchase #3	$151.96	13.382%	$172.2953	$172.30	$172.30	$172.30
Purchase #4	$75.62	3.209%	$78.0466	$78.05	$78.05	$78.00
Purchase #5	$132.35	9.302%	$144.6612	$144.66	$144.65	$144.70
Purchase #6	$77.70	7.207%	$83.2998	$83.30	$83.30	$83.30
Purchase #7	$37.79	10.249%	$41.6631	$41.66	$41.65	$41.70
7 purchase totals =	$775.73		$849.2052	$849.21	$849.20	$849.20