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	$214.55	12.251%	$240.8345	$240.83	$240.85	$240.80
Purchase #2	$112.96	9.525%	$123.7194	$123.72	$123.70	$123.70
Purchase #3	$193.57	7.482%	$208.0529	$208.05	$208.05	$208.10
Purchase #4	$172.43	10.347%	$190.2713	$190.27	$190.25	$190.30
Purchase #5	$170.89	6.243%	$181.5587	$181.56	$181.55	$181.60
Purchase #6	$184.96	11.120%	$205.5276	$205.53	$205.55	$205.50
Purchase #7	$110.33	10.213%	$121.598	$121.60	$121.60	$121.60
7 purchase totals =	$1,159.69		$1,271.5624	$1,271.56	$1,271.55	$1,271.60