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	$134.60	6.839%	$143.8053	$143.81	$143.80	$143.80
Purchase #2	$30.34	4.415%	$31.6795	$31.68	$31.70	$31.70
Purchase #3	$171.85	9.301%	$187.8338	$187.83	$187.85	$187.80
Purchase #4	$37.43	12.656%	$42.1671	$42.17	$42.15	$42.20
Purchase #5	$183.33	3.616%	$189.9592	$189.96	$189.95	$190.00
Purchase #6	$51.67	3.807%	$53.6371	$53.64	$53.65	$53.60
Purchase #7	$157.33	8.382%	$170.5174	$170.52	$170.50	$170.50
7 purchase totals =	$766.55		$819.5994	$819.61	$819.60	$819.60