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	$89.69	12.378%	$100.7918	$100.79	$100.80	$100.80
Purchase #2	$127.30	4.393%	$132.8923	$132.89	$132.90	$132.90
Purchase #3	$176.32	7.322%	$189.2302	$189.23	$189.25	$189.20
Purchase #4	$163.57	6.244%	$173.7833	$173.78	$173.80	$173.80
Purchase #5	$143.88	9.322%	$157.2925	$157.29	$157.30	$157.30
Purchase #6	$142.38	11.417%	$158.6355	$158.64	$158.65	$158.60
Purchase #7	$68.81	3.655%	$71.325	$71.33	$71.35	$71.30
7 purchase totals =	$911.95		$983.9506	$983.95	$984.05	$983.90