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	$146.90	10.174%	$161.8456	$161.85	$161.85	$161.80
Purchase #2	$211.65	12.566%	$238.2459	$238.25	$238.25	$238.20
Purchase #3	$191.38	4.425%	$199.8486	$199.85	$199.85	$199.80
Purchase #4	$105.53	5.277%	$111.0988	$111.10	$111.10	$111.10
Purchase #5	$90.40	11.611%	$100.8963	$100.90	$100.90	$100.90
Purchase #6	$142.86	8.854%	$155.5088	$155.51	$155.50	$155.50
Purchase #7	$17.73	5.195%	$18.6511	$18.65	$18.65	$18.70
7 purchase totals =	$906.45		$986.0951	$986.11	$986.10	$986.00