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	$162.88	6.285%	$173.117	$173.12	$173.10	$173.10
Purchase #2	$45.45	10.626%	$50.2795	$50.28	$50.30	$50.30
Purchase #3	$209.99	8.313%	$227.4465	$227.45	$227.45	$227.40
Purchase #4	$9.59	13.835%	$10.9168	$10.92	$10.90	$10.90
Purchase #5	$64.51	11.385%	$71.8545	$71.85	$71.85	$71.90
Purchase #6	$195.53	5.155%	$205.6096	$205.61	$205.60	$205.60
Purchase #7	$47.79	5.624%	$50.4777	$50.48	$50.50	$50.50
7 purchase totals =	$735.74		$789.7016	$789.71	$789.70	$789.70