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	$83.41	8.654%	$90.6283	$90.63	$90.65	$90.60
Purchase #2	$219.87	12.199%	$246.6919	$246.69	$246.70	$246.70
Purchase #3	$20.87	4.399%	$21.7881	$21.79	$21.80	$21.80
Purchase #4	$19.81	8.616%	$21.5168	$21.52	$21.50	$21.50
Purchase #5	$48.74	3.690%	$50.5385	$50.54	$50.55	$50.50
Purchase #6	$40.69	9.675%	$44.6268	$44.63	$44.65	$44.60
Purchase #7	$43.70	6.294%	$46.4505	$46.45	$46.45	$46.50
7 purchase totals =	$477.09		$522.2409	$522.25	$522.30	$522.20