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	$237.72	7.391%	$255.2899	$255.29	$255.30	$255.30
Purchase #2	$31.96	6.840%	$34.1461	$34.15	$34.15	$34.10
Purchase #3	$20.73	3.784%	$21.5144	$21.51	$21.50	$21.50
Purchase #4	$93.35	7.730%	$100.566	$100.57	$100.55	$100.60
Purchase #5	$15.89	4.417%	$16.5919	$16.59	$16.60	$16.60
Purchase #6	$74.75	6.230%	$79.4069	$79.41	$79.40	$79.40
Purchase #7	$83.71	6.828%	$89.4257	$89.43	$89.45	$89.40
7 purchase totals =	$558.11		$596.9409	$596.95	$596.95	$596.90