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	$106.27	5.613%	$112.2349	$112.23	$112.25	$112.20
Purchase #2	$85.91	5.472%	$90.611	$90.61	$90.60	$90.60
Purchase #3	$144.65	7.316%	$155.2326	$155.23	$155.25	$155.20
Purchase #4	$142.46	5.201%	$149.8693	$149.87	$149.85	$149.90
Purchase #5	$195.64	10.685%	$216.5441	$216.54	$216.55	$216.50
Purchase #6	$215.54	8.319%	$233.4708	$233.47	$233.45	$233.50
Purchase #7	$36.48	11.247%	$40.5829	$40.58	$40.60	$40.60
7 purchase totals =	$926.95		$998.5456	$998.53	$998.55	$998.50