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	$46.30	12.472%	$52.0745	$52.07	$52.05	$52.10
Purchase #2	$59.91	10.183%	$66.0106	$66.01	$66.00	$66.00
Purchase #3	$106.61	4.534%	$111.4437	$111.44	$111.45	$111.40
Purchase #4	$247.95	8.320%	$268.5794	$268.58	$268.60	$268.60
Purchase #5	$33.70	11.599%	$37.6089	$37.61	$37.60	$37.60
Purchase #6	$63.99	13.384%	$72.5544	$72.55	$72.55	$72.60
Purchase #7	$220.98	12.831%	$249.3339	$249.33	$249.35	$249.30
7 purchase totals =	$779.44		$857.6054	$857.59	$857.60	$857.60