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	$107.78	8.652%	$117.1051	$117.11	$117.10	$117.10
Purchase #2	$52.88	7.262%	$56.7201	$56.72	$56.70	$56.70
Purchase #3	$127.37	11.795%	$142.3933	$142.39	$142.40	$142.40
Purchase #4	$35.42	6.807%	$37.831	$37.83	$37.85	$37.80
Purchase #5	$196.73	3.626%	$203.8634	$203.86	$203.85	$203.90
Purchase #6	$240.95	11.422%	$268.4713	$268.47	$268.45	$268.50
Purchase #7	$29.99	13.749%	$34.1133	$34.11	$34.10	$34.10
7 purchase totals =	$791.12		$860.4975	$860.49	$860.45	$860.50