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	$53.58	5.651%	$56.6078	$56.61	$56.60	$56.60
Purchase #2	$95.30	3.243%	$98.3906	$98.39	$98.40	$98.40
Purchase #3	$108.78	10.583%	$120.2922	$120.29	$120.30	$120.30
Purchase #4	$59.45	11.728%	$66.4223	$66.42	$66.40	$66.40
Purchase #5	$84.34	4.132%	$87.8249	$87.82	$87.80	$87.80
Purchase #6	$63.54	4.112%	$66.1528	$66.15	$66.15	$66.20
Purchase #7	$162.57	7.262%	$174.3758	$174.38	$174.40	$174.40
7 purchase totals =	$627.56		$670.0664	$670.06	$670.05	$670.10