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	$47.51	5.487%	$50.1169	$50.12	$50.10	$50.10
Purchase #2	$37.92	13.525%	$43.0487	$43.05	$43.05	$43.00
Purchase #3	$84.35	13.625%	$95.8427	$95.84	$95.85	$95.80
Purchase #4	$50.85	5.405%	$53.5984	$53.60	$53.60	$53.60
Purchase #5	$80.43	11.318%	$89.5331	$89.53	$89.55	$89.50
Purchase #6	$46.56	6.345%	$49.5142	$49.51	$49.50	$49.50
Purchase #7	$23.40	10.392%	$25.8317	$25.83	$25.85	$25.80
7 purchase totals =	$371.02		$407.4857	$407.48	$407.50	$407.30