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	$74.47	5.418%	$78.5048	$78.50	$78.50	$78.50
Purchase #2	$154.25	10.493%	$170.4355	$170.44	$170.45	$170.40
Purchase #3	$151.56	13.470%	$171.9751	$171.98	$172.00	$172.00
Purchase #4	$16.63	11.551%	$18.5509	$18.55	$18.55	$18.60
Purchase #5	$40.74	3.525%	$42.1761	$42.18	$42.20	$42.20
Purchase #6	$247.96	6.165%	$263.2467	$263.25	$263.25	$263.20
Purchase #7	$11.64	7.556%	$12.5195	$12.52	$12.50	$12.50
7 purchase totals =	$697.25		$757.4086	$757.42	$757.45	$757.40