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	$165.72	8.535%	$179.8642	$179.86	$179.85	$179.90
Purchase #2	$130.41	6.500%	$138.8867	$138.89	$138.90	$138.90
Purchase #3	$25.97	9.635%	$28.4722	$28.47	$28.45	$28.50
Purchase #4	$119.90	9.507%	$131.2989	$131.30	$131.30	$131.30
Purchase #5	$100.85	5.332%	$106.2273	$106.23	$106.25	$106.20
Purchase #6	$100.57	10.842%	$111.4738	$111.47	$111.45	$111.50
Purchase #7	$230.94	12.528%	$259.8722	$259.87	$259.85	$259.90
7 purchase totals =	$874.36		$956.0953	$956.09	$956.05	$956.20