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	$60.64	9.463%	$66.3784	$66.38	$66.40	$66.40
Purchase #2	$11.59	7.796%	$12.4936	$12.49	$12.50	$12.50
Purchase #3	$133.85	12.524%	$150.6134	$150.61	$150.60	$150.60
Purchase #4	$141.68	3.478%	$146.6076	$146.61	$146.60	$146.60
Purchase #5	$133.77	6.337%	$142.247	$142.25	$142.25	$142.20
Purchase #6	$228.46	5.152%	$240.2303	$240.23	$240.25	$240.20
Purchase #7	$71.66	8.366%	$77.6551	$77.66	$77.65	$77.70
7 purchase totals =	$781.65		$836.2254	$836.23	$836.25	$836.20