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	$147.85	3.142%	$152.4954	$152.50	$152.50	$152.50
Purchase #2	$79.45	4.464%	$82.9966	$83.00	$83.00	$83.00
Purchase #3	$113.51	9.361%	$124.1357	$124.14	$124.15	$124.10
Purchase #4	$153.81	3.295%	$158.878	$158.88	$158.90	$158.90
Purchase #5	$178.39	7.659%	$192.0529	$192.05	$192.05	$192.10
Purchase #6	$127.66	10.699%	$141.3183	$141.32	$141.30	$141.30
Purchase #7	$62.70	4.109%	$65.2763	$65.28	$65.30	$65.30
7 purchase totals =	$863.37		$917.1532	$917.17	$917.20	$917.20