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	$49.51	10.310%	$54.6145	$54.61	$54.60	$54.60
Purchase #2	$143.75	12.686%	$161.9861	$161.99	$162.00	$162.00
Purchase #3	$89.67	11.670%	$100.1345	$100.13	$100.15	$100.10
Purchase #4	$113.28	9.848%	$124.4358	$124.44	$124.45	$124.40
Purchase #5	$243.95	8.406%	$264.4564	$264.46	$264.45	$264.50
Purchase #6	$223.95	11.818%	$250.4164	$250.42	$250.40	$250.40
Purchase #7	$105.57	11.122%	$117.3115	$117.31	$117.30	$117.30
7 purchase totals =	$969.68		$1,073.3552	$1,073.36	$1,073.35	$1,073.30