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	$238.34	12.506%	$268.1468	$268.15	$268.15	$268.10
Purchase #2	$159.45	10.575%	$176.3118	$176.31	$176.30	$176.30
Purchase #3	$160.89	13.186%	$182.105	$182.11	$182.10	$182.10
Purchase #4	$68.42	13.486%	$77.6471	$77.65	$77.65	$77.60
Purchase #5	$55.45	11.825%	$62.007	$62.01	$62.00	$62.00
Purchase #6	$110.42	5.229%	$116.1939	$116.19	$116.20	$116.20
Purchase #7	$43.92	10.632%	$48.5896	$48.59	$48.60	$48.60
7 purchase totals =	$836.89		$931.0012	$931.01	$931.00	$930.90