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	$89.52	12.698%	$100.8872	$100.89	$100.90	$100.90
Purchase #2	$62.83	7.496%	$67.5397	$67.54	$67.55	$67.50
Purchase #3	$198.70	13.426%	$225.3775	$225.38	$225.40	$225.40
Purchase #4	$237.68	3.324%	$245.5805	$245.58	$245.60	$245.60
Purchase #5	$148.50	7.719%	$159.9627	$159.96	$159.95	$160.00
Purchase #6	$182.49	6.718%	$194.7497	$194.75	$194.75	$194.70
Purchase #7	$60.52	3.657%	$62.7332	$62.73	$62.75	$62.70
7 purchase totals =	$980.24		$1,056.8305	$1,056.83	$1,056.90	$1,056.80