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	$33.70	11.692%	$37.6402	$37.64	$37.65	$37.60
Purchase #2	$51.99	9.151%	$56.7476	$56.75	$56.75	$56.70
Purchase #3	$246.41	5.858%	$260.8447	$260.84	$260.85	$260.80
Purchase #4	$157.54	5.583%	$166.3355	$166.34	$166.35	$166.30
Purchase #5	$232.61	13.724%	$264.5334	$264.53	$264.55	$264.50
Purchase #6	$106.64	10.707%	$118.0579	$118.06	$118.05	$118.10
Purchase #7	$86.45	3.383%	$89.3746	$89.37	$89.35	$89.40
7 purchase totals =	$915.34		$993.5339	$993.53	$993.55	$993.40