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	$170.98	8.405%	$185.3509	$185.35	$185.35	$185.40
Purchase #2	$221.60	10.307%	$244.4403	$244.44	$244.45	$244.40
Purchase #3	$5.53	13.632%	$6.2838	$6.28	$6.30	$6.30
Purchase #4	$151.48	11.302%	$168.6003	$168.60	$168.60	$168.60
Purchase #5	$89.50	12.618%	$100.7931	$100.79	$100.80	$100.80
Purchase #6	$108.35	5.595%	$114.4122	$114.41	$114.40	$114.40
Purchase #7	$95.80	9.558%	$104.9566	$104.96	$104.95	$105.00
7 purchase totals =	$843.24		$924.8372	$924.83	$924.85	$924.90