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	$72.90	10.597%	$80.6252	$80.63	$80.65	$80.60
Purchase #2	$19.35	6.109%	$20.5321	$20.53	$20.55	$20.50
Purchase #3	$175.68	5.601%	$185.5198	$185.52	$185.50	$185.50
Purchase #4	$107.57	7.863%	$116.0282	$116.03	$116.05	$116.00
Purchase #5	$167.35	7.230%	$179.4494	$179.45	$179.45	$179.40
Purchase #6	$27.39	8.511%	$29.7212	$29.72	$29.70	$29.70
Purchase #7	$112.45	6.261%	$119.4905	$119.49	$119.50	$119.50
7 purchase totals =	$682.69		$731.3664	$731.37	$731.40	$731.20