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	$29.48	6.274%	$31.3296	$31.33	$31.35	$31.30
Purchase #2	$237.76	4.484%	$248.4212	$248.42	$248.40	$248.40
Purchase #3	$80.53	11.481%	$89.7756	$89.78	$89.80	$89.80
Purchase #4	$47.46	11.619%	$52.9744	$52.97	$52.95	$53.00
Purchase #5	$241.28	9.361%	$263.8662	$263.87	$263.85	$263.90
Purchase #6	$124.52	4.806%	$130.5044	$130.50	$130.50	$130.50
Purchase #7	$160.35	4.521%	$167.5994	$167.60	$167.60	$167.60
7 purchase totals =	$921.38		$984.4708	$984.47	$984.45	$984.50