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	$50.29	6.363%	$53.49	$53.49	$53.50	$53.50
Purchase #2	$139.57	10.762%	$154.5905	$154.59	$154.60	$154.60
Purchase #3	$37.64	12.848%	$42.476	$42.48	$42.50	$42.50
Purchase #4	$49.59	4.594%	$51.8682	$51.87	$51.85	$51.90
Purchase #5	$148.60	3.800%	$154.2468	$154.25	$154.25	$154.20
Purchase #6	$215.73	8.793%	$234.6991	$234.70	$234.70	$234.70
Purchase #7	$130.33	10.683%	$144.2532	$144.25	$144.25	$144.30
7 purchase totals =	$771.75		$835.6238	$835.63	$835.65	$835.70