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	$155.28	13.597%	$176.3934	$176.39	$176.40	$176.40
Purchase #2	$85.46	5.226%	$89.9261	$89.93	$89.95	$89.90
Purchase #3	$150.40	5.243%	$158.2855	$158.29	$158.30	$158.30
Purchase #4	$84.83	3.436%	$87.7448	$87.74	$87.75	$87.70
Purchase #5	$196.94	4.211%	$205.2331	$205.23	$205.25	$205.20
Purchase #6	$76.44	7.674%	$82.306	$82.31	$82.30	$82.30
Purchase #7	$122.55	6.249%	$130.2081	$130.21	$130.20	$130.20
7 purchase totals =	$871.90		$930.0970	$930.10	$930.15	$930.00