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	$170.37	4.597%	$178.2019	$178.20	$178.20	$178.20
Purchase #2	$137.74	9.364%	$150.638	$150.64	$150.65	$150.60
Purchase #3	$210.60	4.397%	$219.8601	$219.86	$219.85	$219.90
Purchase #4	$93.25	13.442%	$105.7847	$105.78	$105.80	$105.80
Purchase #5	$123.44	11.430%	$137.5492	$137.55	$137.55	$137.50
Purchase #6	$60.83	8.571%	$66.0437	$66.04	$66.05	$66.00
Purchase #7	$235.92	7.571%	$253.7815	$253.78	$253.80	$253.80
7 purchase totals =	$1,032.15		$1,111.8591	$1,111.85	$1,111.90	$1,111.80