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	$31.50	5.564%	$33.2527	$33.25	$33.25	$33.30
Purchase #2	$168.91	11.534%	$188.3921	$188.39	$188.40	$188.40
Purchase #3	$64.58	13.615%	$73.3726	$73.37	$73.35	$73.40
Purchase #4	$220.29	8.551%	$239.127	$239.13	$239.15	$239.10
Purchase #5	$99.93	5.444%	$105.3702	$105.37	$105.35	$105.40
Purchase #6	$128.56	13.801%	$146.3026	$146.30	$146.30	$146.30
Purchase #7	$100.46	4.308%	$104.7878	$104.79	$104.80	$104.80
7 purchase totals =	$814.23		$890.6050	$890.60	$890.60	$890.70