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	$71.52	9.168%	$78.077	$78.08	$78.10	$78.10
Purchase #2	$111.87	10.864%	$124.0236	$124.02	$124.00	$124.00
Purchase #3	$125.31	11.384%	$139.5753	$139.58	$139.60	$139.60
Purchase #4	$177.98	12.108%	$199.5298	$199.53	$199.55	$199.50
Purchase #5	$50.85	3.707%	$52.735	$52.74	$52.75	$52.70
Purchase #6	$78.81	3.385%	$81.4777	$81.48	$81.50	$81.50
Purchase #7	$43.84	6.124%	$46.5248	$46.52	$46.50	$46.50
7 purchase totals =	$660.18		$721.9432	$721.95	$722.00	$721.90