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	$140.35	13.217%	$158.9001	$158.90	$158.90	$158.90
Purchase #2	$179.79	5.406%	$189.5094	$189.51	$189.50	$189.50
Purchase #3	$134.66	11.621%	$150.3088	$150.31	$150.30	$150.30
Purchase #4	$170.80	11.141%	$189.8288	$189.83	$189.85	$189.80
Purchase #5	$65.38	9.176%	$71.3793	$71.38	$71.40	$71.40
Purchase #6	$27.73	7.354%	$29.7693	$29.77	$29.75	$29.80
Purchase #7	$130.64	6.111%	$138.6234	$138.62	$138.60	$138.60
7 purchase totals =	$849.35		$928.3191	$928.32	$928.30	$928.30