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	$64.93	13.849%	$73.9222	$73.92	$73.90	$73.90
Purchase #2	$109.35	10.149%	$120.4479	$120.45	$120.45	$120.40
Purchase #3	$22.76	13.126%	$25.7475	$25.75	$25.75	$25.70
Purchase #4	$141.47	6.275%	$150.3472	$150.35	$150.35	$150.30
Purchase #5	$76.99	7.167%	$82.5079	$82.51	$82.50	$82.50
Purchase #6	$65.96	9.336%	$72.118	$72.12	$72.10	$72.10
Purchase #7	$49.60	8.146%	$53.6404	$53.64	$53.65	$53.60
7 purchase totals =	$531.06		$578.7311	$578.74	$578.70	$578.50