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	$142.55	3.512%	$147.5564	$147.56	$147.55	$147.60
Purchase #2	$135.36	13.674%	$153.8691	$153.87	$153.85	$153.90
Purchase #3	$126.54	12.536%	$142.4031	$142.40	$142.40	$142.40
Purchase #4	$5.30	12.288%	$5.9513	$5.95	$5.95	$6.00
Purchase #5	$86.86	4.137%	$90.4534	$90.45	$90.45	$90.50
Purchase #6	$74.64	5.298%	$78.5944	$78.59	$78.60	$78.60
Purchase #7	$242.92	11.599%	$271.0963	$271.10	$271.10	$271.10
7 purchase totals =	$814.17		$889.9240	$889.92	$889.90	$890.10