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	$141.60	6.537%	$150.8564	$150.86	$150.85	$150.90
Purchase #2	$62.90	11.552%	$70.1662	$70.17	$70.15	$70.20
Purchase #3	$117.67	13.329%	$133.3542	$133.35	$133.35	$133.40
Purchase #4	$77.61	9.798%	$85.2142	$85.21	$85.20	$85.20
Purchase #5	$19.27	10.388%	$21.2718	$21.27	$21.25	$21.30
Purchase #6	$155.87	6.807%	$166.4801	$166.48	$166.50	$166.50
Purchase #7	$64.54	12.759%	$72.7747	$72.77	$72.75	$72.80
7 purchase totals =	$639.46		$700.1176	$700.11	$700.05	$700.30