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	$159.28	7.666%	$171.4904	$171.49	$171.50	$171.50
Purchase #2	$242.89	9.309%	$265.5006	$265.50	$265.50	$265.50
Purchase #3	$22.62	8.370%	$24.5133	$24.51	$24.50	$24.50
Purchase #4	$138.62	7.419%	$148.9042	$148.90	$148.90	$148.90
Purchase #5	$186.36	4.329%	$194.4275	$194.43	$194.45	$194.40
Purchase #6	$113.37	12.543%	$127.59	$127.59	$127.60	$127.60
Purchase #7	$18.49	10.706%	$20.4695	$20.47	$20.45	$20.50
7 purchase totals =	$881.63		$952.8955	$952.89	$952.90	$952.90