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	$49.97	9.632%	$54.7831	$54.78	$54.80	$54.80
Purchase #2	$134.97	3.660%	$139.9099	$139.91	$139.90	$139.90
Purchase #3	$73.93	11.242%	$82.2412	$82.24	$82.25	$82.20
Purchase #4	$183.64	11.478%	$204.7182	$204.72	$204.70	$204.70
Purchase #5	$166.85	11.193%	$185.5255	$185.53	$185.55	$185.50
Purchase #6	$56.95	4.727%	$59.642	$59.64	$59.65	$59.60
Purchase #7	$177.70	11.162%	$197.5349	$197.53	$197.55	$197.50
7 purchase totals =	$844.01		$924.3548	$924.35	$924.40	$924.20