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	$168.53	12.808%	$190.1153	$190.12	$190.10	$190.10
Purchase #2	$90.85	13.199%	$102.8413	$102.84	$102.85	$102.80
Purchase #3	$19.77	7.641%	$21.2806	$21.28	$21.30	$21.30
Purchase #4	$111.48	10.630%	$123.3303	$123.33	$123.35	$123.30
Purchase #5	$93.75	13.397%	$106.3097	$106.31	$106.30	$106.30
Purchase #6	$76.52	3.766%	$79.4017	$79.40	$79.40	$79.40
Purchase #7	$92.67	4.230%	$96.5899	$96.59	$96.60	$96.60
7 purchase totals =	$653.57		$719.8688	$719.87	$719.90	$719.80