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	$203.58	8.769%	$221.4319	$221.43	$221.45	$221.40
Purchase #2	$163.32	5.609%	$172.4806	$172.48	$172.50	$172.50
Purchase #3	$131.25	6.377%	$139.6198	$139.62	$139.60	$139.60
Purchase #4	$191.27	5.219%	$201.2524	$201.25	$201.25	$201.30
Purchase #5	$102.86	10.792%	$113.9607	$113.96	$113.95	$114.00
Purchase #6	$48.33	4.829%	$50.6639	$50.66	$50.65	$50.70
Purchase #7	$91.70	9.601%	$100.5041	$100.50	$100.50	$100.50
7 purchase totals =	$932.31		$999.9134	$999.90	$999.90	$1,000.00