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	$80.93	10.535%	$89.456	$89.46	$89.45	$89.50
Purchase #2	$40.94	13.482%	$46.4595	$46.46	$46.45	$46.50
Purchase #3	$13.39	12.150%	$15.0169	$15.02	$15.00	$15.00
Purchase #4	$111.96	12.287%	$125.7165	$125.72	$125.70	$125.70
Purchase #5	$9.60	7.656%	$10.335	$10.34	$10.35	$10.30
Purchase #6	$171.49	13.638%	$194.8778	$194.88	$194.90	$194.90
Purchase #7	$59.99	3.488%	$62.0825	$62.08	$62.10	$62.10
7 purchase totals =	$488.30		$543.9442	$543.96	$543.95	$544.00