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	$48.29	13.674%	$54.8932	$54.89	$54.90	$54.90
Purchase #2	$202.95	11.106%	$225.4896	$225.49	$225.50	$225.50
Purchase #3	$36.70	4.144%	$38.2208	$38.22	$38.20	$38.20
Purchase #4	$209.73	9.829%	$230.3444	$230.34	$230.35	$230.30
Purchase #5	$125.54	13.434%	$142.405	$142.41	$142.40	$142.40
Purchase #6	$16.30	13.455%	$18.4932	$18.49	$18.50	$18.50
Purchase #7	$25.89	7.169%	$27.7461	$27.75	$27.75	$27.70
7 purchase totals =	$665.40		$737.5923	$737.59	$737.60	$737.50