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	$48.78	4.782%	$51.1127	$51.11	$51.10	$51.10
Purchase #2	$188.27	5.820%	$199.2273	$199.23	$199.25	$199.20
Purchase #3	$182.70	4.273%	$190.5068	$190.51	$190.50	$190.50
Purchase #4	$184.52	6.272%	$196.0931	$196.09	$196.10	$196.10
Purchase #5	$61.82	13.376%	$70.089	$70.09	$70.10	$70.10
Purchase #6	$14.59	5.833%	$15.441	$15.44	$15.45	$15.40
Purchase #7	$107.77	10.161%	$118.7205	$118.72	$118.70	$118.70
7 purchase totals =	$788.45		$841.1904	$841.19	$841.20	$841.10