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	$135.61	9.280%	$148.1946	$148.19	$148.20	$148.20
Purchase #2	$209.60	8.364%	$227.1309	$227.13	$227.15	$227.10
Purchase #3	$105.28	5.275%	$110.8335	$110.83	$110.85	$110.80
Purchase #4	$76.40	11.621%	$85.2784	$85.28	$85.30	$85.30
Purchase #5	$102.56	8.315%	$111.0879	$111.09	$111.10	$111.10
Purchase #6	$229.98	10.285%	$253.6334	$253.63	$253.65	$253.60
Purchase #7	$38.93	4.632%	$40.7332	$40.73	$40.75	$40.70
7 purchase totals =	$898.36		$976.8919	$976.88	$977.00	$976.80