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	$117.59	13.141%	$133.0425	$133.04	$133.05	$133.00
Purchase #2	$167.87	11.665%	$187.452	$187.45	$187.45	$187.50
Purchase #3	$56.93	4.304%	$59.3803	$59.38	$59.40	$59.40
Purchase #4	$207.94	7.773%	$224.1032	$224.10	$224.10	$224.10
Purchase #5	$18.87	6.539%	$20.1039	$20.10	$20.10	$20.10
Purchase #6	$93.42	3.487%	$96.6776	$96.68	$96.70	$96.70
Purchase #7	$131.85	10.776%	$146.0582	$146.06	$146.05	$146.10
7 purchase totals =	$794.47		$866.8177	$866.81	$866.85	$866.90