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	$116.57	10.535%	$128.8506	$128.85	$128.85	$128.90
Purchase #2	$19.92	5.664%	$21.0483	$21.05	$21.05	$21.00
Purchase #3	$210.57	9.310%	$230.1741	$230.17	$230.15	$230.20
Purchase #4	$131.91	9.288%	$144.1618	$144.16	$144.15	$144.20
Purchase #5	$94.55	10.636%	$104.6063	$104.61	$104.60	$104.60
Purchase #6	$230.38	6.717%	$245.8546	$245.85	$245.85	$245.90
Purchase #7	$248.35	13.151%	$281.0105	$281.01	$281.00	$281.00
7 purchase totals =	$1,052.25		$1,155.7062	$1,155.70	$1,155.65	$1,155.80