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	$45.48	11.626%	$50.7675	$50.77	$50.75	$50.80
Purchase #2	$95.98	7.864%	$103.5279	$103.53	$103.55	$103.50
Purchase #3	$71.36	10.290%	$78.7029	$78.70	$78.70	$78.70
Purchase #4	$43.58	5.219%	$45.8544	$45.85	$45.85	$45.90
Purchase #5	$132.89	5.828%	$140.6348	$140.63	$140.65	$140.60
Purchase #6	$239.84	8.149%	$259.3846	$259.38	$259.40	$259.40
Purchase #7	$138.47	9.585%	$151.7423	$151.74	$151.75	$151.70
7 purchase totals =	$767.60		$830.6144	$830.60	$830.65	$830.60