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	$131.89	9.253%	$144.0938	$144.09	$144.10	$144.10
Purchase #2	$237.89	13.836%	$270.8045	$270.80	$270.80	$270.80
Purchase #3	$202.47	4.797%	$212.1825	$212.18	$212.20	$212.20
Purchase #4	$176.50	5.303%	$185.8598	$185.86	$185.85	$185.90
Purchase #5	$137.52	11.657%	$153.5507	$153.55	$153.55	$153.60
Purchase #6	$155.59	5.619%	$164.3326	$164.33	$164.35	$164.30
Purchase #7	$208.37	5.281%	$219.374	$219.37	$219.35	$219.40
7 purchase totals =	$1,250.23		$1,350.1979	$1,350.18	$1,350.20	$1,350.30