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	$27.28	11.849%	$30.5124	$30.51	$30.50	$30.50
Purchase #2	$93.25	7.611%	$100.3473	$100.35	$100.35	$100.30
Purchase #3	$167.55	10.642%	$185.3807	$185.38	$185.40	$185.40
Purchase #4	$12.68	8.369%	$13.7412	$13.74	$13.75	$13.70
Purchase #5	$203.72	9.762%	$223.6071	$223.61	$223.60	$223.60
Purchase #6	$58.91	11.687%	$65.7948	$65.79	$65.80	$65.80
Purchase #7	$185.97	5.500%	$196.1984	$196.20	$196.20	$196.20
7 purchase totals =	$749.36		$815.5819	$815.58	$815.60	$815.50