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	$94.29	12.266%	$105.8556	$105.86	$105.85	$105.90
Purchase #2	$33.85	10.513%	$37.4087	$37.41	$37.40	$37.40
Purchase #3	$123.94	6.278%	$131.721	$131.72	$131.70	$131.70
Purchase #4	$143.45	8.671%	$155.8885	$155.89	$155.90	$155.90
Purchase #5	$129.38	3.118%	$133.4141	$133.41	$133.40	$133.40
Purchase #6	$31.38	11.228%	$34.9033	$34.90	$34.90	$34.90
Purchase #7	$226.73	3.259%	$234.1191	$234.12	$234.10	$234.10
7 purchase totals =	$783.02		$833.3103	$833.31	$833.25	$833.30