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	$153.78	7.245%	$164.9214	$164.92	$164.90	$164.90
Purchase #2	$131.71	11.566%	$146.9436	$146.94	$146.95	$146.90
Purchase #3	$245.87	9.740%	$269.8177	$269.82	$269.80	$269.80
Purchase #4	$158.94	4.868%	$166.6772	$166.68	$166.70	$166.70
Purchase #5	$200.45	5.688%	$211.8516	$211.85	$211.85	$211.90
Purchase #6	$137.60	9.697%	$150.9431	$150.94	$150.95	$150.90
Purchase #7	$73.72	9.166%	$80.4772	$80.48	$80.50	$80.50
7 purchase totals =	$1,102.07		$1,191.6318	$1,191.63	$1,191.65	$1,191.60