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	$14.74	9.419%	$16.1284	$16.13	$16.15	$16.10
Purchase #2	$160.69	7.736%	$173.121	$173.12	$173.10	$173.10
Purchase #3	$56.71	4.118%	$59.0453	$59.05	$59.05	$59.00
Purchase #4	$203.68	10.691%	$225.4554	$225.46	$225.45	$225.50
Purchase #5	$95.80	13.792%	$109.0127	$109.01	$109.00	$109.00
Purchase #6	$163.42	4.839%	$171.3279	$171.33	$171.35	$171.30
Purchase #7	$144.82	6.723%	$154.5562	$154.56	$154.55	$154.60
7 purchase totals =	$839.86		$908.6469	$908.66	$908.65	$908.60