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	$80.85	11.637%	$90.2585	$90.26	$90.25	$90.30
Purchase #2	$156.90	9.131%	$171.2265	$171.23	$171.25	$171.20
Purchase #3	$150.48	5.120%	$158.1846	$158.18	$158.20	$158.20
Purchase #4	$250.27	13.726%	$284.6221	$284.62	$284.60	$284.60
Purchase #5	$166.89	13.527%	$189.4652	$189.47	$189.45	$189.50
Purchase #6	$233.81	10.653%	$258.7178	$258.72	$258.70	$258.70
Purchase #7	$57.62	7.870%	$62.1547	$62.15	$62.15	$62.20
7 purchase totals =	$1,096.82		$1,214.6294	$1,214.63	$1,214.60	$1,214.70