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	$170.99	12.649%	$192.6185	$192.62	$192.60	$192.60
Purchase #2	$178.90	9.818%	$196.4644	$196.46	$196.45	$196.50
Purchase #3	$62.30	5.802%	$65.9146	$65.91	$65.90	$65.90
Purchase #4	$95.86	8.716%	$104.2152	$104.22	$104.20	$104.20
Purchase #5	$166.70	4.485%	$174.1765	$174.18	$174.20	$174.20
Purchase #6	$16.41	12.710%	$18.4957	$18.50	$18.50	$18.50
Purchase #7	$159.64	3.263%	$164.8491	$164.85	$164.85	$164.80
7 purchase totals =	$850.80		$916.7340	$916.74	$916.70	$916.70