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	$54.60	4.607%	$57.1154	$57.12	$57.10	$57.10
Purchase #2	$43.69	3.277%	$45.1217	$45.12	$45.10	$45.10
Purchase #3	$166.67	8.269%	$180.4519	$180.45	$180.45	$180.50
Purchase #4	$30.58	9.597%	$33.5148	$33.51	$33.50	$33.50
Purchase #5	$93.43	10.806%	$103.526	$103.53	$103.55	$103.50
Purchase #6	$38.96	3.311%	$40.25	$40.25	$40.25	$40.30
Purchase #7	$175.59	10.521%	$194.0638	$194.06	$194.05	$194.10
7 purchase totals =	$603.52		$654.0436	$654.04	$654.00	$654.10