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	$225.78	13.331%	$255.8787	$255.88	$255.90	$255.90
Purchase #2	$122.92	8.859%	$133.8095	$133.81	$133.80	$133.80
Purchase #3	$154.46	11.653%	$172.4592	$172.46	$172.45	$172.50
Purchase #4	$237.88	12.498%	$267.6102	$267.61	$267.60	$267.60
Purchase #5	$99.98	5.767%	$105.7458	$105.75	$105.75	$105.70
Purchase #6	$100.79	9.174%	$110.0365	$110.04	$110.05	$110.00
Purchase #7	$83.41	12.651%	$93.9622	$93.96	$93.95	$94.00
7 purchase totals =	$1,025.22		$1,139.5021	$1,139.51	$1,139.50	$1,139.50