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	$54.58	8.309%	$59.1151	$59.12	$59.10	$59.10
Purchase #2	$66.68	11.589%	$74.4075	$74.41	$74.40	$74.40
Purchase #3	$182.89	7.187%	$196.0343	$196.03	$196.05	$196.00
Purchase #4	$158.32	10.269%	$174.5779	$174.58	$174.60	$174.60
Purchase #5	$48.48	9.494%	$53.0827	$53.08	$53.10	$53.10
Purchase #6	$155.41	8.249%	$168.2298	$168.23	$168.25	$168.20
Purchase #7	$94.72	11.375%	$105.4944	$105.49	$105.50	$105.50
7 purchase totals =	$761.08		$830.9417	$830.94	$831.00	$830.90