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	$90.94	12.681%	$102.4721	$102.47	$102.45	$102.50
Purchase #2	$118.87	7.222%	$127.4548	$127.45	$127.45	$127.50
Purchase #3	$103.30	3.394%	$106.806	$106.81	$106.80	$106.80
Purchase #4	$100.29	9.623%	$109.9409	$109.94	$109.95	$109.90
Purchase #5	$29.43	9.451%	$32.2114	$32.21	$32.20	$32.20
Purchase #6	$31.43	8.103%	$33.9768	$33.98	$34.00	$34.00
Purchase #7	$132.57	9.757%	$145.5049	$145.50	$145.50	$145.50
7 purchase totals =	$606.83		$658.3669	$658.36	$658.35	$658.40