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	$89.77	12.397%	$100.8988	$100.90	$100.90	$100.90
Purchase #2	$20.58	4.704%	$21.5481	$21.55	$21.55	$21.50
Purchase #3	$155.60	3.274%	$160.6943	$160.69	$160.70	$160.70
Purchase #4	$99.96	5.685%	$105.6427	$105.64	$105.65	$105.60
Purchase #5	$142.92	11.818%	$159.8103	$159.81	$159.80	$159.80
Purchase #6	$215.40	12.667%	$242.6847	$242.68	$242.70	$242.70
Purchase #7	$169.66	7.532%	$182.4388	$182.44	$182.45	$182.40
7 purchase totals =	$893.89		$973.7177	$973.71	$973.75	$973.60