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	$169.69	5.251%	$178.6004	$178.60	$178.60	$178.60
Purchase #2	$195.40	12.729%	$220.2725	$220.27	$220.25	$220.30
Purchase #3	$90.42	13.843%	$102.9368	$102.94	$102.95	$102.90
Purchase #4	$138.71	5.296%	$146.0561	$146.06	$146.05	$146.10
Purchase #5	$84.82	6.520%	$90.3503	$90.35	$90.35	$90.40
Purchase #6	$54.74	8.509%	$59.3978	$59.40	$59.40	$59.40
Purchase #7	$69.41	12.804%	$78.2973	$78.30	$78.30	$78.30
7 purchase totals =	$803.19		$875.9112	$875.92	$875.90	$876.00