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	$164.58	9.102%	$179.5601	$179.56	$179.55	$179.60
Purchase #2	$151.76	7.333%	$162.8886	$162.89	$162.90	$162.90
Purchase #3	$126.61	5.514%	$133.5913	$133.59	$133.60	$133.60
Purchase #4	$58.28	11.196%	$64.805	$64.81	$64.80	$64.80
Purchase #5	$55.48	12.336%	$62.324	$62.32	$62.30	$62.30
Purchase #6	$85.79	10.397%	$94.7096	$94.71	$94.70	$94.70
Purchase #7	$80.72	12.569%	$90.8657	$90.87	$90.85	$90.90
7 purchase totals =	$723.22		$788.7443	$788.75	$788.70	$788.80