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	$149.75	12.447%	$168.3894	$168.39	$168.40	$168.40
Purchase #2	$164.25	8.543%	$178.2819	$178.28	$178.30	$178.30
Purchase #3	$32.79	13.501%	$37.217	$37.22	$37.20	$37.20
Purchase #4	$75.93	9.774%	$83.3514	$83.35	$83.35	$83.40
Purchase #5	$159.50	8.531%	$173.1069	$173.11	$173.10	$173.10
Purchase #6	$191.54	7.870%	$206.6142	$206.61	$206.60	$206.60
Purchase #7	$132.77	8.113%	$143.5416	$143.54	$143.55	$143.50
7 purchase totals =	$906.53		$990.5024	$990.50	$990.50	$990.50