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	$236.94	6.552%	$252.4643	$252.46	$252.45	$252.50
Purchase #2	$162.31	4.512%	$169.6334	$169.63	$169.65	$169.60
Purchase #3	$76.90	12.852%	$86.7832	$86.78	$86.80	$86.80
Purchase #4	$109.48	12.578%	$123.2504	$123.25	$123.25	$123.30
Purchase #5	$7.51	4.543%	$7.8512	$7.85	$7.85	$7.90
Purchase #6	$229.72	8.404%	$249.0257	$249.03	$249.05	$249.00
Purchase #7	$75.83	7.422%	$81.4581	$81.46	$81.45	$81.50
7 purchase totals =	$898.69		$970.4663	$970.46	$970.50	$970.60