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	$131.44	11.843%	$147.0064	$147.01	$147.00	$147.00
Purchase #2	$197.35	10.528%	$218.127	$218.13	$218.15	$218.10
Purchase #3	$149.51	6.153%	$158.7094	$158.71	$158.70	$158.70
Purchase #4	$132.76	10.211%	$146.3161	$146.32	$146.30	$146.30
Purchase #5	$137.49	13.275%	$155.7418	$155.74	$155.75	$155.70
Purchase #6	$163.61	10.782%	$181.2504	$181.25	$181.25	$181.30
Purchase #7	$89.52	4.455%	$93.5081	$93.51	$93.50	$93.50
7 purchase totals =	$1,001.68		$1,100.6592	$1,100.67	$1,100.65	$1,100.60