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	$91.62	12.105%	$102.7106	$102.71	$102.70	$102.70
Purchase #2	$69.31	4.527%	$72.4477	$72.45	$72.45	$72.40
Purchase #3	$92.47	8.721%	$100.5343	$100.53	$100.55	$100.50
Purchase #4	$142.71	3.623%	$147.8804	$147.88	$147.90	$147.90
Purchase #5	$128.96	11.533%	$143.833	$143.83	$143.85	$143.80
Purchase #6	$159.47	10.402%	$176.0581	$176.06	$176.05	$176.10
Purchase #7	$207.65	8.380%	$225.0511	$225.05	$225.05	$225.10
7 purchase totals =	$892.19		$968.5152	$968.51	$968.55	$968.50