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	$243.96	10.569%	$269.7441	$269.74	$269.75	$269.70
Purchase #2	$197.76	5.509%	$208.6546	$208.65	$208.65	$208.70
Purchase #3	$39.60	7.555%	$42.5918	$42.59	$42.60	$42.60
Purchase #4	$242.72	7.669%	$261.3342	$261.33	$261.35	$261.30
Purchase #5	$187.88	6.371%	$199.8498	$199.85	$199.85	$199.80
Purchase #6	$41.28	10.323%	$45.5413	$45.54	$45.55	$45.50
Purchase #7	$235.34	10.575%	$260.2272	$260.23	$260.25	$260.20
7 purchase totals =	$1,188.54		$1,287.9430	$1,287.93	$1,288.00	$1,287.80