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	$16.52	9.804%	$18.1396	$18.14	$18.15	$18.10
Purchase #2	$35.50	5.419%	$37.4237	$37.42	$37.40	$37.40
Purchase #3	$79.29	11.626%	$88.5083	$88.51	$88.50	$88.50
Purchase #4	$91.99	13.866%	$104.7453	$104.75	$104.75	$104.70
Purchase #5	$97.89	11.728%	$109.3705	$109.37	$109.35	$109.40
Purchase #6	$29.69	10.763%	$32.8855	$32.89	$32.90	$32.90
Purchase #7	$115.73	9.574%	$126.81	$126.81	$126.80	$126.80
7 purchase totals =	$466.61		$517.8829	$517.89	$517.85	$517.80