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	$54.62	12.258%	$61.3153	$61.32	$61.30	$61.30
Purchase #2	$28.99	12.271%	$32.5474	$32.55	$32.55	$32.50
Purchase #3	$164.30	3.644%	$170.2871	$170.29	$170.30	$170.30
Purchase #4	$60.64	10.656%	$67.1018	$67.10	$67.10	$67.10
Purchase #5	$198.93	11.223%	$221.2559	$221.26	$221.25	$221.30
Purchase #6	$246.77	13.824%	$280.8835	$280.88	$280.90	$280.90
Purchase #7	$113.63	11.830%	$127.0724	$127.07	$127.05	$127.10
7 purchase totals =	$867.88		$960.4634	$960.47	$960.45	$960.50