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	$11.98	5.282%	$12.6128	$12.61	$12.60	$12.60
Purchase #2	$208.40	4.477%	$217.7301	$217.73	$217.75	$217.70
Purchase #3	$22.69	6.183%	$24.0929	$24.09	$24.10	$24.10
Purchase #4	$100.49	5.228%	$105.7436	$105.74	$105.75	$105.70
Purchase #5	$92.82	7.541%	$99.8196	$99.82	$99.80	$99.80
Purchase #6	$157.28	6.779%	$167.942	$167.94	$167.95	$167.90
Purchase #7	$18.35	5.553%	$19.369	$19.37	$19.35	$19.40
7 purchase totals =	$612.01		$647.3100	$647.30	$647.30	$647.20