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	$48.75	11.847%	$54.5254	$54.53	$54.55	$54.50
Purchase #2	$39.55	7.504%	$42.5178	$42.52	$42.50	$42.50
Purchase #3	$138.94	5.139%	$146.0801	$146.08	$146.10	$146.10
Purchase #4	$51.93	8.513%	$56.3508	$56.35	$56.35	$56.40
Purchase #5	$181.98	13.503%	$206.5528	$206.55	$206.55	$206.60
Purchase #6	$184.62	11.610%	$206.0544	$206.05	$206.05	$206.10
Purchase #7	$53.69	5.837%	$56.8239	$56.82	$56.80	$56.80
7 purchase totals =	$699.46		$768.9052	$768.90	$768.90	$769.00