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	$26.67	11.819%	$29.8221	$29.82	$29.80	$29.80
Purchase #2	$191.44	7.226%	$205.2735	$205.27	$205.25	$205.30
Purchase #3	$169.36	10.852%	$187.7389	$187.74	$187.75	$187.70
Purchase #4	$93.86	12.727%	$105.8056	$105.81	$105.80	$105.80
Purchase #5	$226.31	12.637%	$254.9088	$254.91	$254.90	$254.90
Purchase #6	$38.64	4.767%	$40.482	$40.48	$40.50	$40.50
Purchase #7	$10.54	3.582%	$10.9175	$10.92	$10.90	$10.90
7 purchase totals =	$756.82		$834.9484	$834.95	$834.90	$834.90