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	$148.84	11.854%	$166.4835	$166.48	$166.50	$166.50
Purchase #2	$58.68	11.863%	$65.6412	$65.64	$65.65	$65.60
Purchase #3	$230.42	5.323%	$242.6853	$242.69	$242.70	$242.70
Purchase #4	$177.75	10.477%	$196.3729	$196.37	$196.35	$196.40
Purchase #5	$11.44	8.359%	$12.3963	$12.40	$12.40	$12.40
Purchase #6	$218.74	9.142%	$238.7372	$238.74	$238.75	$238.70
Purchase #7	$240.27	7.397%	$258.0428	$258.04	$258.05	$258.00
7 purchase totals =	$1,086.14		$1,180.3592	$1,180.36	$1,180.40	$1,180.30