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	$32.70	13.246%	$37.0314	$37.03	$37.05	$37.00
Purchase #2	$20.85	10.829%	$23.1078	$23.11	$23.10	$23.10
Purchase #3	$238.72	11.590%	$266.3876	$266.39	$266.40	$266.40
Purchase #4	$162.88	9.509%	$178.3683	$178.37	$178.35	$178.40
Purchase #5	$119.31	7.315%	$128.0375	$128.04	$128.05	$128.00
Purchase #6	$99.68	3.657%	$103.3253	$103.33	$103.35	$103.30
Purchase #7	$64.72	3.572%	$67.0318	$67.03	$67.05	$67.00
7 purchase totals =	$738.86		$803.2897	$803.30	$803.35	$803.20