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	$76.74	5.266%	$80.7811	$80.78	$80.80	$80.80
Purchase #2	$20.79	3.587%	$21.5357	$21.54	$21.55	$21.50
Purchase #3	$13.54	5.599%	$14.2981	$14.30	$14.30	$14.30
Purchase #4	$146.97	13.417%	$166.689	$166.69	$166.70	$166.70
Purchase #5	$190.26	12.390%	$213.8332	$213.83	$213.85	$213.80
Purchase #6	$88.77	12.728%	$100.0686	$100.07	$100.05	$100.10
Purchase #7	$40.72	13.733%	$46.3121	$46.31	$46.30	$46.30
7 purchase totals =	$577.79		$643.5178	$643.52	$643.55	$643.50