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	$112.26	9.618%	$123.0572	$123.06	$123.05	$123.10
Purchase #2	$139.88	9.610%	$153.3225	$153.32	$153.30	$153.30
Purchase #3	$152.65	4.803%	$159.9818	$159.98	$160.00	$160.00
Purchase #4	$10.83	10.598%	$11.9778	$11.98	$12.00	$12.00
Purchase #5	$227.34	6.802%	$242.8037	$242.80	$242.80	$242.80
Purchase #6	$35.77	13.305%	$40.5292	$40.53	$40.55	$40.50
Purchase #7	$90.87	11.808%	$101.5999	$101.60	$101.60	$101.60
7 purchase totals =	$769.60		$833.2721	$833.27	$833.30	$833.30