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	$72.55	7.820%	$78.2234	$78.22	$78.20	$78.20
Purchase #2	$14.34	5.604%	$15.1436	$15.14	$15.15	$15.10
Purchase #3	$225.99	13.146%	$255.6986	$255.70	$255.70	$255.70
Purchase #4	$144.31	7.508%	$155.1448	$155.14	$155.15	$155.10
Purchase #5	$149.66	8.488%	$162.3631	$162.36	$162.35	$162.40
Purchase #6	$16.48	12.374%	$18.5192	$18.52	$18.50	$18.50
Purchase #7	$155.64	4.272%	$162.2889	$162.29	$162.30	$162.30
7 purchase totals =	$778.97		$847.3816	$847.37	$847.35	$847.30