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	$243.68	9.692%	$267.2975	$267.30	$267.30	$267.30
Purchase #2	$151.35	8.873%	$164.7793	$164.78	$164.80	$164.80
Purchase #3	$182.55	12.564%	$205.4856	$205.49	$205.50	$205.50
Purchase #4	$137.33	9.327%	$150.1388	$150.14	$150.15	$150.10
Purchase #5	$22.60	11.561%	$25.2128	$25.21	$25.20	$25.20
Purchase #6	$172.98	8.353%	$187.429	$187.43	$187.45	$187.40
Purchase #7	$100.29	10.685%	$111.006	$111.01	$111.00	$111.00
7 purchase totals =	$1,010.78		$1,111.3490	$1,111.36	$1,111.40	$1,111.30