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	$104.50	3.706%	$108.3728	$108.37	$108.35	$108.40
Purchase #2	$25.27	7.284%	$27.1107	$27.11	$27.10	$27.10
Purchase #3	$166.30	7.272%	$178.3933	$178.39	$178.40	$178.40
Purchase #4	$148.60	5.555%	$156.8547	$156.85	$156.85	$156.90
Purchase #5	$66.52	9.311%	$72.7137	$72.71	$72.70	$72.70
Purchase #6	$187.44	5.774%	$198.2628	$198.26	$198.25	$198.30
Purchase #7	$150.87	5.352%	$158.9446	$158.94	$158.95	$158.90
7 purchase totals =	$849.50		$900.6526	$900.63	$900.60	$900.70