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	$19.50	4.639%	$20.4046	$20.40	$20.40	$20.40
Purchase #2	$52.63	13.190%	$59.5719	$59.57	$59.55	$59.60
Purchase #3	$123.91	11.850%	$138.5933	$138.59	$138.60	$138.60
Purchase #4	$32.77	3.370%	$33.8743	$33.87	$33.85	$33.90
Purchase #5	$169.90	13.124%	$192.1977	$192.20	$192.20	$192.20
Purchase #6	$224.42	10.642%	$248.3028	$248.30	$248.30	$248.30
Purchase #7	$232.58	3.863%	$241.5646	$241.56	$241.55	$241.60
7 purchase totals =	$855.71		$934.5092	$934.49	$934.45	$934.60