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	$38.26	3.440%	$39.5761	$39.58	$39.60	$39.60
Purchase #2	$104.30	3.687%	$108.1455	$108.15	$108.15	$108.10
Purchase #3	$69.69	12.434%	$78.3553	$78.36	$78.35	$78.40
Purchase #4	$152.89	3.722%	$158.5806	$158.58	$158.60	$158.60
Purchase #5	$11.66	10.371%	$12.8693	$12.87	$12.85	$12.90
Purchase #6	$183.62	3.185%	$189.4683	$189.47	$189.45	$189.50
Purchase #7	$238.74	13.492%	$270.9508	$270.95	$270.95	$271.00
7 purchase totals =	$799.16		$857.9459	$857.96	$857.95	$858.10