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	$12.35	10.480%	$13.6443	$13.64	$13.65	$13.60
Purchase #2	$130.65	7.545%	$140.5075	$140.51	$140.50	$140.50
Purchase #3	$6.34	13.147%	$7.1735	$7.17	$7.15	$7.20
Purchase #4	$53.47	11.758%	$59.757	$59.76	$59.75	$59.80
Purchase #5	$14.27	10.206%	$15.7264	$15.73	$15.75	$15.70
Purchase #6	$62.59	12.667%	$70.5183	$70.52	$70.50	$70.50
Purchase #7	$96.51	8.489%	$104.7027	$104.70	$104.70	$104.70
7 purchase totals =	$376.18		$412.0297	$412.03	$412.00	$412.00