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	$63.56	6.857%	$67.9183	$67.92	$67.90	$67.90
Purchase #2	$66.66	12.287%	$74.8505	$74.85	$74.85	$74.90
Purchase #3	$55.75	6.366%	$59.299	$59.30	$59.30	$59.30
Purchase #4	$138.76	3.340%	$143.3946	$143.39	$143.40	$143.40
Purchase #5	$76.87	11.673%	$85.843	$85.84	$85.85	$85.80
Purchase #6	$70.60	10.625%	$78.1013	$78.10	$78.10	$78.10
Purchase #7	$19.87	11.441%	$22.1433	$22.14	$22.15	$22.10
7 purchase totals =	$492.07		$531.5500	$531.54	$531.55	$531.50