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	$171.99	4.225%	$179.2566	$179.26	$179.25	$179.30
Purchase #2	$212.60	8.211%	$230.0566	$230.06	$230.05	$230.10
Purchase #3	$183.80	6.874%	$196.4344	$196.43	$196.45	$196.40
Purchase #4	$229.97	11.281%	$255.9129	$255.91	$255.90	$255.90
Purchase #5	$170.70	11.730%	$190.7231	$190.72	$190.70	$190.70
Purchase #6	$148.92	4.198%	$155.1717	$155.17	$155.15	$155.20
Purchase #7	$174.57	5.599%	$184.3442	$184.34	$184.35	$184.30
7 purchase totals =	$1,292.55		$1,391.8995	$1,391.89	$1,391.85	$1,391.90