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	$148.60	12.724%	$167.5079	$167.51	$167.50	$167.50
Purchase #2	$146.60	13.821%	$166.8616	$166.86	$166.85	$166.90
Purchase #3	$225.94	13.113%	$255.5675	$255.57	$255.55	$255.60
Purchase #4	$66.77	11.519%	$74.4612	$74.46	$74.45	$74.50
Purchase #5	$77.95	5.224%	$82.0221	$82.02	$82.00	$82.00
Purchase #6	$237.54	7.425%	$255.1773	$255.18	$255.20	$255.20
Purchase #7	$234.70	4.158%	$244.4588	$244.46	$244.45	$244.50
7 purchase totals =	$1,138.10		$1,246.0564	$1,246.06	$1,246.00	$1,246.20