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	$76.96	8.287%	$83.3377	$83.34	$83.35	$83.30
Purchase #2	$137.27	10.519%	$151.7094	$151.71	$151.70	$151.70
Purchase #3	$22.43	7.463%	$24.104	$24.10	$24.10	$24.10
Purchase #4	$45.54	12.476%	$51.2216	$51.22	$51.20	$51.20
Purchase #5	$231.58	11.766%	$258.8277	$258.83	$258.85	$258.80
Purchase #6	$104.81	10.828%	$116.1588	$116.16	$116.15	$116.20
Purchase #7	$224.96	11.399%	$250.6032	$250.60	$250.60	$250.60
7 purchase totals =	$843.55		$935.9624	$935.96	$935.95	$935.90