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	$125.84	9.311%	$137.557	$137.56	$137.55	$137.60
Purchase #2	$79.99	10.774%	$88.6081	$88.61	$88.60	$88.60
Purchase #3	$37.51	7.852%	$40.4553	$40.46	$40.45	$40.50
Purchase #4	$205.33	4.865%	$215.3193	$215.32	$215.30	$215.30
Purchase #5	$137.70	11.491%	$153.5231	$153.52	$153.50	$153.50
Purchase #6	$120.64	4.707%	$126.3185	$126.32	$126.30	$126.30
Purchase #7	$139.64	8.482%	$151.4843	$151.48	$151.50	$151.50
7 purchase totals =	$846.65		$913.2656	$913.27	$913.20	$913.30