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	$77.64	7.619%	$83.5554	$83.56	$83.55	$83.60
Purchase #2	$131.28	5.666%	$138.7183	$138.72	$138.70	$138.70
Purchase #3	$78.80	8.852%	$85.7754	$85.78	$85.80	$85.80
Purchase #4	$86.40	9.391%	$94.5138	$94.51	$94.50	$94.50
Purchase #5	$192.86	11.394%	$214.8345	$214.83	$214.85	$214.80
Purchase #6	$232.76	10.700%	$257.6653	$257.67	$257.65	$257.70
Purchase #7	$134.39	8.294%	$145.5363	$145.54	$145.55	$145.50
7 purchase totals =	$934.13		$1,020.5990	$1,020.61	$1,020.60	$1,020.60