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	$151.39	3.106%	$156.0922	$156.09	$156.10	$156.10
Purchase #2	$140.27	3.695%	$145.453	$145.45	$145.45	$145.50
Purchase #3	$104.58	7.819%	$112.7571	$112.76	$112.75	$112.80
Purchase #4	$20.29	11.154%	$22.5531	$22.55	$22.55	$22.60
Purchase #5	$245.55	9.671%	$269.2971	$269.30	$269.30	$269.30
Purchase #6	$139.89	13.225%	$158.3905	$158.39	$158.40	$158.40
Purchase #7	$167.71	12.425%	$188.548	$188.55	$188.55	$188.50
7 purchase totals =	$969.68		$1,053.0910	$1,053.09	$1,053.10	$1,053.20