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	$61.59	12.791%	$69.468	$69.47	$69.45	$69.50
Purchase #2	$247.76	11.247%	$275.6256	$275.63	$275.65	$275.60
Purchase #3	$49.48	13.763%	$56.2899	$56.29	$56.30	$56.30
Purchase #4	$166.25	5.226%	$174.9382	$174.94	$174.95	$174.90
Purchase #5	$81.40	10.752%	$90.1521	$90.15	$90.15	$90.20
Purchase #6	$31.94	3.205%	$32.9637	$32.96	$32.95	$33.00
Purchase #7	$241.84	3.523%	$250.36	$250.36	$250.35	$250.40
7 purchase totals =	$880.26		$949.7975	$949.80	$949.80	$949.90