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	$17.72	3.653%	$18.3673	$18.37	$18.35	$18.40
Purchase #2	$174.27	7.280%	$186.9569	$186.96	$186.95	$187.00
Purchase #3	$172.29	8.245%	$186.4953	$186.50	$186.50	$186.50
Purchase #4	$105.29	7.747%	$113.4468	$113.45	$113.45	$113.40
Purchase #5	$44.81	11.247%	$49.8498	$49.85	$49.85	$49.80
Purchase #6	$141.59	6.244%	$150.4309	$150.43	$150.45	$150.40
Purchase #7	$53.52	3.352%	$55.314	$55.31	$55.30	$55.30
7 purchase totals =	$709.49		$760.8610	$760.87	$760.85	$760.80