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	$46.99	8.117%	$50.8042	$50.80	$50.80	$50.80
Purchase #2	$63.73	5.557%	$67.2715	$67.27	$67.25	$67.30
Purchase #3	$43.74	11.739%	$48.8746	$48.87	$48.85	$48.90
Purchase #4	$108.82	6.232%	$115.6017	$115.60	$115.60	$115.60
Purchase #5	$20.53	4.431%	$21.4397	$21.44	$21.45	$21.40
Purchase #6	$105.89	13.757%	$120.4573	$120.46	$120.45	$120.50
Purchase #7	$150.60	9.586%	$165.0365	$165.04	$165.05	$165.00
7 purchase totals =	$540.30		$589.4855	$589.48	$589.45	$589.50