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	$68.29	6.527%	$72.7473	$72.75	$72.75	$72.70
Purchase #2	$224.90	13.539%	$255.3492	$255.35	$255.35	$255.30
Purchase #3	$118.28	8.185%	$127.9612	$127.96	$127.95	$128.00
Purchase #4	$59.78	10.315%	$65.9463	$65.95	$65.95	$65.90
Purchase #5	$119.76	11.537%	$133.5767	$133.58	$133.60	$133.60
Purchase #6	$138.87	12.221%	$155.8413	$155.84	$155.85	$155.80
Purchase #7	$156.36	5.866%	$165.5321	$165.53	$165.55	$165.50
7 purchase totals =	$886.24		$976.9541	$976.96	$977.00	$976.80