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	$70.39	13.870%	$80.1531	$80.15	$80.15	$80.20
Purchase #2	$175.30	5.767%	$185.4096	$185.41	$185.40	$185.40
Purchase #3	$55.51	5.326%	$58.4665	$58.47	$58.45	$58.50
Purchase #4	$97.55	9.871%	$107.1792	$107.18	$107.20	$107.20
Purchase #5	$140.64	4.211%	$146.5624	$146.56	$146.55	$146.60
Purchase #6	$62.92	7.484%	$67.6289	$67.63	$67.65	$67.60
Purchase #7	$61.51	7.774%	$66.2918	$66.29	$66.30	$66.30
7 purchase totals =	$663.82		$711.6915	$711.69	$711.70	$711.80