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	$17.30	8.128%	$18.7061	$18.71	$18.70	$18.70
Purchase #2	$17.86	4.785%	$18.7146	$18.71	$18.70	$18.70
Purchase #3	$38.39	11.386%	$42.7611	$42.76	$42.75	$42.80
Purchase #4	$222.90	3.391%	$230.4585	$230.46	$230.45	$230.50
Purchase #5	$82.33	4.478%	$86.0167	$86.02	$86.00	$86.00
Purchase #6	$171.85	9.271%	$187.7822	$187.78	$187.80	$187.80
Purchase #7	$250.99	12.260%	$281.7614	$281.76	$281.75	$281.80
7 purchase totals =	$801.62		$866.2006	$866.20	$866.15	$866.30