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	$162.83	12.792%	$183.6592	$183.66	$183.65	$183.70
Purchase #2	$115.46	6.201%	$122.6197	$122.62	$122.60	$122.60
Purchase #3	$7.29	12.832%	$8.2255	$8.23	$8.25	$8.20
Purchase #4	$70.47	12.827%	$79.5092	$79.51	$79.50	$79.50
Purchase #5	$71.66	10.170%	$78.9478	$78.95	$78.95	$78.90
Purchase #6	$64.90	4.439%	$67.7809	$67.78	$67.80	$67.80
Purchase #7	$40.27	6.433%	$42.8606	$42.86	$42.85	$42.90
7 purchase totals =	$532.88		$583.6029	$583.61	$583.60	$583.60