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	$56.67	4.233%	$59.0688	$59.07	$59.05	$59.10
Purchase #2	$143.99	5.437%	$151.8187	$151.82	$151.80	$151.80
Purchase #3	$106.92	4.805%	$112.0575	$112.06	$112.05	$112.10
Purchase #4	$16.59	10.288%	$18.2968	$18.30	$18.30	$18.30
Purchase #5	$134.51	13.106%	$152.1389	$152.14	$152.15	$152.10
Purchase #6	$149.79	4.592%	$156.6684	$156.67	$156.65	$156.70
Purchase #7	$149.67	12.604%	$168.5344	$168.53	$168.55	$168.50
7 purchase totals =	$758.14		$818.5835	$818.59	$818.55	$818.60