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	$49.90	10.508%	$55.1435	$55.14	$55.15	$55.10
Purchase #2	$143.45	9.212%	$156.6646	$156.66	$156.65	$156.70
Purchase #3	$53.38	3.240%	$55.1095	$55.11	$55.10	$55.10
Purchase #4	$19.66	4.850%	$20.6135	$20.61	$20.60	$20.60
Purchase #5	$173.39	13.322%	$196.489	$196.49	$196.50	$196.50
Purchase #6	$30.61	5.606%	$32.326	$32.33	$32.35	$32.30
Purchase #7	$152.53	7.691%	$164.2611	$164.26	$164.25	$164.30
7 purchase totals =	$622.92		$680.6072	$680.60	$680.60	$680.60