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	$100.81	10.480%	$111.3749	$111.37	$111.35	$111.40
Purchase #2	$89.54	12.463%	$100.6994	$100.70	$100.70	$100.70
Purchase #3	$223.43	12.427%	$251.1956	$251.20	$251.20	$251.20
Purchase #4	$208.48	3.151%	$215.0492	$215.05	$215.05	$215.00
Purchase #5	$143.36	10.380%	$158.2408	$158.24	$158.25	$158.20
Purchase #6	$21.33	9.514%	$23.3593	$23.36	$23.35	$23.40
Purchase #7	$34.64	9.495%	$37.9291	$37.93	$37.95	$37.90
7 purchase totals =	$821.59		$897.8483	$897.85	$897.85	$897.80