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	$8.32	3.296%	$8.5942	$8.59	$8.60	$8.60
Purchase #2	$171.45	4.571%	$179.287	$179.29	$179.30	$179.30
Purchase #3	$168.76	6.382%	$179.5303	$179.53	$179.55	$179.50
Purchase #4	$81.64	4.466%	$85.286	$85.29	$85.30	$85.30
Purchase #5	$61.73	10.109%	$67.9703	$67.97	$67.95	$68.00
Purchase #6	$51.64	10.853%	$57.2445	$57.24	$57.25	$57.20
Purchase #7	$240.55	11.529%	$268.283	$268.28	$268.30	$268.30
7 purchase totals =	$784.09		$846.1953	$846.19	$846.25	$846.20