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	$20.32	4.493%	$21.233	$21.23	$21.25	$21.20
Purchase #2	$15.32	12.265%	$17.199	$17.20	$17.20	$17.20
Purchase #3	$154.48	6.285%	$164.1891	$164.19	$164.20	$164.20
Purchase #4	$92.77	8.175%	$100.3539	$100.35	$100.35	$100.40
Purchase #5	$70.91	12.227%	$79.5802	$79.58	$79.60	$79.60
Purchase #6	$62.79	6.515%	$66.8808	$66.88	$66.90	$66.90
Purchase #7	$43.88	6.192%	$46.597	$46.60	$46.60	$46.60
7 purchase totals =	$460.47		$496.0330	$496.03	$496.10	$496.10