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	$235.34	5.729%	$248.8226	$248.82	$248.80	$248.80
Purchase #2	$78.49	5.131%	$82.5173	$82.52	$82.50	$82.50
Purchase #3	$200.93	11.105%	$223.2433	$223.24	$223.25	$223.20
Purchase #4	$214.66	11.397%	$239.1248	$239.12	$239.10	$239.10
Purchase #5	$76.88	7.832%	$82.9012	$82.90	$82.90	$82.90
Purchase #6	$106.41	9.651%	$116.6796	$116.68	$116.70	$116.70
Purchase #7	$36.78	8.482%	$39.8997	$39.90	$39.90	$39.90
7 purchase totals =	$949.49		$1,033.1885	$1,033.18	$1,033.15	$1,033.10