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	$86.72	10.445%	$95.7779	$95.78	$95.80	$95.80
Purchase #2	$185.55	5.160%	$195.1244	$195.12	$195.10	$195.10
Purchase #3	$99.99	9.227%	$109.2161	$109.22	$109.20	$109.20
Purchase #4	$157.72	10.659%	$174.5314	$174.53	$174.55	$174.50
Purchase #5	$99.37	8.671%	$107.9864	$107.99	$108.00	$108.00
Purchase #6	$104.85	4.328%	$109.3879	$109.39	$109.40	$109.40
Purchase #7	$105.75	11.171%	$117.5633	$117.56	$117.55	$117.60
7 purchase totals =	$839.95		$909.5874	$909.59	$909.60	$909.60