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	$203.50	5.445%	$214.5806	$214.58	$214.60	$214.60
Purchase #2	$145.85	10.265%	$160.8215	$160.82	$160.80	$160.80
Purchase #3	$96.68	9.437%	$105.8037	$105.80	$105.80	$105.80
Purchase #4	$115.85	6.250%	$123.0906	$123.09	$123.10	$123.10
Purchase #5	$129.56	8.455%	$140.5143	$140.51	$140.50	$140.50
Purchase #6	$57.71	3.710%	$59.851	$59.85	$59.85	$59.90
Purchase #7	$190.78	7.174%	$204.4666	$204.47	$204.45	$204.50
7 purchase totals =	$939.93		$1,009.1283	$1,009.12	$1,009.10	$1,009.20