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	$168.50	5.616%	$177.963	$177.96	$177.95	$178.00
Purchase #2	$160.55	8.842%	$174.7458	$174.75	$174.75	$174.70
Purchase #3	$89.34	13.351%	$101.2678	$101.27	$101.25	$101.30
Purchase #4	$37.42	9.119%	$40.8323	$40.83	$40.85	$40.80
Purchase #5	$28.54	11.243%	$31.7488	$31.75	$31.75	$31.70
Purchase #6	$10.27	13.810%	$11.6883	$11.69	$11.70	$11.70
Purchase #7	$99.83	3.813%	$103.6365	$103.64	$103.65	$103.60
7 purchase totals =	$594.45		$641.8825	$641.89	$641.90	$641.80