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	$26.46	7.539%	$28.4548	$28.45	$28.45	$28.50
Purchase #2	$158.51	7.328%	$170.1256	$170.13	$170.15	$170.10
Purchase #3	$24.33	4.160%	$25.3421	$25.34	$25.35	$25.30
Purchase #4	$104.50	9.561%	$114.4912	$114.49	$114.50	$114.50
Purchase #5	$116.59	6.394%	$124.0448	$124.04	$124.05	$124.00
Purchase #6	$77.54	10.393%	$85.5987	$85.60	$85.60	$85.60
Purchase #7	$164.33	4.416%	$171.5868	$171.59	$171.60	$171.60
7 purchase totals =	$672.26		$719.6440	$719.64	$719.70	$719.60