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	$72.99	12.426%	$82.0597	$82.06	$82.05	$82.10
Purchase #2	$212.65	4.588%	$222.4064	$222.41	$222.40	$222.40
Purchase #3	$37.82	10.686%	$41.8614	$41.86	$41.85	$41.90
Purchase #4	$74.66	11.248%	$83.0578	$83.06	$83.05	$83.10
Purchase #5	$18.26	3.286%	$18.86	$18.86	$18.85	$18.90
Purchase #6	$138.89	5.401%	$146.3914	$146.39	$146.40	$146.40
Purchase #7	$234.52	11.321%	$261.07	$261.07	$261.05	$261.10
7 purchase totals =	$789.79		$855.7067	$855.71	$855.65	$855.90