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	$243.50	5.402%	$256.6539	$256.65	$256.65	$256.70
Purchase #2	$243.97	5.182%	$256.6125	$256.61	$256.60	$256.60
Purchase #3	$200.31	11.387%	$223.1193	$223.12	$223.10	$223.10
Purchase #4	$5.92	13.703%	$6.7312	$6.73	$6.75	$6.70
Purchase #5	$194.28	7.219%	$208.3051	$208.31	$208.30	$208.30
Purchase #6	$13.60	6.721%	$14.5141	$14.51	$14.50	$14.50
Purchase #7	$13.76	13.476%	$15.6143	$15.61	$15.60	$15.60
7 purchase totals =	$915.34		$981.5504	$981.54	$981.50	$981.50