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	$49.27	11.111%	$54.7444	$54.74	$54.75	$54.70
Purchase #2	$205.56	8.752%	$223.5506	$223.55	$223.55	$223.60
Purchase #3	$165.83	4.221%	$172.8297	$172.83	$172.85	$172.80
Purchase #4	$82.65	3.539%	$85.575	$85.58	$85.60	$85.60
Purchase #5	$74.38	8.711%	$80.8592	$80.86	$80.85	$80.90
Purchase #6	$72.59	5.208%	$76.3705	$76.37	$76.35	$76.40
Purchase #7	$106.56	11.164%	$118.4564	$118.46	$118.45	$118.50
7 purchase totals =	$756.84		$812.3858	$812.39	$812.40	$812.50