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	$34.63	11.351%	$38.5609	$38.56	$38.55	$38.60
Purchase #2	$46.28	6.254%	$49.1744	$49.17	$49.15	$49.20
Purchase #3	$18.28	10.720%	$20.2396	$20.24	$20.25	$20.20
Purchase #4	$202.82	6.665%	$216.338	$216.34	$216.35	$216.30
Purchase #5	$209.85	4.491%	$219.2744	$219.27	$219.25	$219.30
Purchase #6	$105.96	13.778%	$120.5592	$120.56	$120.55	$120.60
Purchase #7	$173.85	6.693%	$185.4858	$185.49	$185.50	$185.50
7 purchase totals =	$791.67		$849.6323	$849.63	$849.60	$849.70