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	$231.27	8.493%	$250.9118	$250.91	$250.90	$250.90
Purchase #2	$140.37	7.479%	$150.8683	$150.87	$150.85	$150.90
Purchase #3	$166.27	6.793%	$177.5647	$177.56	$177.55	$177.60
Purchase #4	$70.74	10.826%	$78.3983	$78.40	$78.40	$78.40
Purchase #5	$38.29	9.118%	$41.7813	$41.78	$41.80	$41.80
Purchase #6	$15.98	4.122%	$16.6387	$16.64	$16.65	$16.60
Purchase #7	$118.82	10.326%	$131.0894	$131.09	$131.10	$131.10
7 purchase totals =	$781.74		$847.2525	$847.25	$847.25	$847.30