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	$242.39	5.451%	$255.6027	$255.60	$255.60	$255.60
Purchase #2	$170.50	12.795%	$192.3155	$192.32	$192.30	$192.30
Purchase #3	$131.41	6.382%	$139.7966	$139.80	$139.80	$139.80
Purchase #4	$245.35	9.867%	$269.5587	$269.56	$269.55	$269.60
Purchase #5	$226.59	12.726%	$255.4258	$255.43	$255.45	$255.40
Purchase #6	$165.37	8.252%	$179.0163	$179.02	$179.00	$179.00
Purchase #7	$96.89	11.193%	$107.7349	$107.73	$107.75	$107.70
7 purchase totals =	$1,278.50		$1,399.4505	$1,399.46	$1,399.45	$1,399.40