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	$10.31	6.346%	$10.9643	$10.96	$10.95	$11.00
Purchase #2	$63.56	4.689%	$66.5403	$66.54	$66.55	$66.50
Purchase #3	$115.85	6.289%	$123.1358	$123.14	$123.15	$123.10
Purchase #4	$70.88	13.191%	$80.2298	$80.23	$80.25	$80.20
Purchase #5	$23.31	6.535%	$24.8333	$24.83	$24.85	$24.80
Purchase #6	$138.73	10.700%	$153.5741	$153.57	$153.55	$153.60
Purchase #7	$103.26	3.404%	$106.775	$106.78	$106.80	$106.80
7 purchase totals =	$525.90		$566.0526	$566.05	$566.10	$566.00