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	$228.76	11.684%	$255.4883	$255.49	$255.50	$255.50
Purchase #2	$69.50	7.609%	$74.7883	$74.79	$74.80	$74.80
Purchase #3	$56.36	6.215%	$59.8628	$59.86	$59.85	$59.90
Purchase #4	$177.69	12.211%	$199.3877	$199.39	$199.40	$199.40
Purchase #5	$43.28	6.611%	$46.1412	$46.14	$46.15	$46.10
Purchase #6	$27.94	5.548%	$29.4901	$29.49	$29.50	$29.50
Purchase #7	$84.73	9.619%	$92.8802	$92.88	$92.90	$92.90
7 purchase totals =	$688.26		$758.0386	$758.04	$758.10	$758.10