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	$183.42	12.584%	$206.5016	$206.50	$206.50	$206.50
Purchase #2	$199.62	7.754%	$215.0985	$215.10	$215.10	$215.10
Purchase #3	$196.68	13.701%	$223.6271	$223.63	$223.65	$223.60
Purchase #4	$37.88	12.495%	$42.6131	$42.61	$42.60	$42.60
Purchase #5	$49.72	4.795%	$52.1041	$52.10	$52.10	$52.10
Purchase #6	$67.85	7.217%	$72.7467	$72.75	$72.75	$72.70
Purchase #7	$40.97	3.759%	$42.5101	$42.51	$42.50	$42.50
7 purchase totals =	$776.14		$855.2012	$855.20	$855.20	$855.10