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	$137.42	3.761%	$142.5884	$142.59	$142.60	$142.60
Purchase #2	$248.87	4.743%	$260.6739	$260.67	$260.65	$260.70
Purchase #3	$238.55	9.621%	$261.5009	$261.50	$261.50	$261.50
Purchase #4	$152.89	10.152%	$168.4114	$168.41	$168.40	$168.40
Purchase #5	$132.50	3.459%	$137.0832	$137.08	$137.10	$137.10
Purchase #6	$76.58	13.430%	$86.8647	$86.86	$86.85	$86.90
Purchase #7	$134.56	5.619%	$142.1209	$142.12	$142.10	$142.10
7 purchase totals =	$1,121.37		$1,199.2434	$1,199.23	$1,199.20	$1,199.30