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	$72.57	9.667%	$79.5853	$79.59	$79.60	$79.60
Purchase #2	$193.79	5.767%	$204.9659	$204.97	$204.95	$205.00
Purchase #3	$107.48	5.538%	$113.4322	$113.43	$113.45	$113.40
Purchase #4	$46.70	11.721%	$52.1737	$52.17	$52.15	$52.20
Purchase #5	$221.51	13.211%	$250.7737	$250.77	$250.75	$250.80
Purchase #6	$52.50	13.316%	$59.4909	$59.49	$59.50	$59.50
Purchase #7	$63.61	10.699%	$70.4156	$70.42	$70.40	$70.40
7 purchase totals =	$758.16		$830.8373	$830.84	$830.80	$830.90