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	$220.60	13.614%	$250.6325	$250.63	$250.65	$250.60
Purchase #2	$143.27	12.648%	$161.3908	$161.39	$161.40	$161.40
Purchase #3	$132.90	8.640%	$144.3826	$144.38	$144.40	$144.40
Purchase #4	$52.47	4.613%	$54.8904	$54.89	$54.90	$54.90
Purchase #5	$202.45	13.472%	$229.7241	$229.72	$229.70	$229.70
Purchase #6	$138.57	13.684%	$157.5319	$157.53	$157.55	$157.50
Purchase #7	$139.90	8.796%	$152.2056	$152.21	$152.20	$152.20
7 purchase totals =	$1,030.16		$1,150.7579	$1,150.75	$1,150.80	$1,150.70