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	$23.89	12.657%	$26.9138	$26.91	$26.90	$26.90
Purchase #2	$43.52	4.742%	$45.5837	$45.58	$45.60	$45.60
Purchase #3	$146.98	10.508%	$162.4247	$162.42	$162.40	$162.40
Purchase #4	$74.82	5.174%	$78.6912	$78.69	$78.70	$78.70
Purchase #5	$120.45	8.384%	$130.5485	$130.55	$130.55	$130.50
Purchase #6	$18.55	12.147%	$20.8033	$20.80	$20.80	$20.80
Purchase #7	$49.72	4.327%	$51.8714	$51.87	$51.85	$51.90
7 purchase totals =	$477.93		$516.8366	$516.82	$516.80	$516.80