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	$71.83	9.141%	$78.396	$78.40	$78.40	$78.40
Purchase #2	$101.86	12.103%	$114.1881	$114.19	$114.20	$114.20
Purchase #3	$142.51	9.751%	$156.4062	$156.41	$156.40	$156.40
Purchase #4	$125.82	3.186%	$129.8286	$129.83	$129.85	$129.80
Purchase #5	$156.25	9.786%	$171.5406	$171.54	$171.55	$171.50
Purchase #6	$149.45	13.130%	$169.0728	$169.07	$169.05	$169.10
Purchase #7	$19.49	4.314%	$20.3308	$20.33	$20.35	$20.30
7 purchase totals =	$767.21		$839.7631	$839.77	$839.80	$839.70