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	$131.63	5.670%	$139.0934	$139.09	$139.10	$139.10
Purchase #2	$41.46	5.139%	$43.5906	$43.59	$43.60	$43.60
Purchase #3	$75.27	9.617%	$82.5087	$82.51	$82.50	$82.50
Purchase #4	$168.78	8.457%	$183.0537	$183.05	$183.05	$183.10
Purchase #5	$162.73	7.617%	$175.1251	$175.13	$175.15	$175.10
Purchase #6	$119.86	11.834%	$134.0442	$134.04	$134.05	$134.00
Purchase #7	$159.64	12.341%	$179.3412	$179.34	$179.35	$179.30
7 purchase totals =	$859.37		$936.7569	$936.75	$936.80	$936.70