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	$44.88	10.198%	$49.4569	$49.46	$49.45	$49.50
Purchase #2	$54.59	12.730%	$61.5393	$61.54	$61.55	$61.50
Purchase #3	$166.61	5.526%	$175.8169	$175.82	$175.80	$175.80
Purchase #4	$200.53	11.635%	$223.8617	$223.86	$223.85	$223.90
Purchase #5	$53.77	10.533%	$59.4336	$59.43	$59.45	$59.40
Purchase #6	$122.36	12.748%	$137.9585	$137.96	$137.95	$138.00
Purchase #7	$202.40	12.191%	$227.0746	$227.07	$227.05	$227.10
7 purchase totals =	$845.14		$935.1415	$935.14	$935.10	$935.20