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	$165.93	4.151%	$172.8178	$172.82	$172.80	$172.80
Purchase #2	$58.59	11.866%	$65.5423	$65.54	$65.55	$65.50
Purchase #3	$45.86	7.839%	$49.455	$49.46	$49.45	$49.50
Purchase #4	$228.32	10.182%	$251.5675	$251.57	$251.55	$251.60
Purchase #5	$190.77	4.319%	$199.0094	$199.01	$199.00	$199.00
Purchase #6	$47.93	10.724%	$53.07	$53.07	$53.05	$53.10
Purchase #7	$223.27	10.599%	$246.9344	$246.93	$246.95	$246.90
7 purchase totals =	$960.67		$1,038.3964	$1,038.40	$1,038.35	$1,038.40