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	$18.28	3.395%	$18.9006	$18.90	$18.90	$18.90
Purchase #2	$107.33	12.603%	$120.8568	$120.86	$120.85	$120.90
Purchase #3	$187.84	10.814%	$208.153	$208.15	$208.15	$208.20
Purchase #4	$28.32	10.556%	$31.3095	$31.31	$31.30	$31.30
Purchase #5	$102.27	8.566%	$111.0304	$111.03	$111.05	$111.00
Purchase #6	$167.65	9.545%	$183.6522	$183.65	$183.65	$183.70
Purchase #7	$134.46	5.228%	$141.4896	$141.49	$141.50	$141.50
7 purchase totals =	$746.15		$815.3921	$815.39	$815.40	$815.50