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	$144.94	12.855%	$163.572	$163.57	$163.55	$163.60
Purchase #2	$164.45	12.723%	$185.373	$185.37	$185.35	$185.40
Purchase #3	$94.60	7.636%	$101.8237	$101.82	$101.80	$101.80
Purchase #4	$192.61	3.857%	$200.039	$200.04	$200.05	$200.00
Purchase #5	$198.28	11.821%	$221.7187	$221.72	$221.70	$221.70
Purchase #6	$70.50	10.154%	$77.6586	$77.66	$77.65	$77.70
Purchase #7	$234.49	6.769%	$250.3626	$250.36	$250.35	$250.40
7 purchase totals =	$1,099.87		$1,200.5476	$1,200.54	$1,200.45	$1,200.60