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	$185.39	13.159%	$209.7855	$209.79	$209.80	$209.80
Purchase #2	$200.26	8.286%	$216.8535	$216.85	$216.85	$216.90
Purchase #3	$61.87	13.763%	$70.3852	$70.39	$70.40	$70.40
Purchase #4	$70.75	11.664%	$79.0023	$79.00	$79.00	$79.00
Purchase #5	$111.78	10.286%	$123.2777	$123.28	$123.30	$123.30
Purchase #6	$84.32	13.209%	$95.4578	$95.46	$95.45	$95.50
Purchase #7	$170.46	9.710%	$187.0117	$187.01	$187.00	$187.00
7 purchase totals =	$884.83		$981.7737	$981.78	$981.80	$981.90