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	$51.50	6.563%	$54.8799	$54.88	$54.90	$54.90
Purchase #2	$196.90	12.189%	$220.9001	$220.90	$220.90	$220.90
Purchase #3	$212.53	9.681%	$233.105	$233.11	$233.10	$233.10
Purchase #4	$23.75	6.286%	$25.2429	$25.24	$25.25	$25.20
Purchase #5	$56.39	5.339%	$59.4007	$59.40	$59.40	$59.40
Purchase #6	$113.49	8.442%	$123.0708	$123.07	$123.05	$123.10
Purchase #7	$124.90	10.704%	$138.2693	$138.27	$138.25	$138.30
7 purchase totals =	$779.46		$854.8687	$854.87	$854.85	$854.90