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	$228.31	13.746%	$259.6935	$259.69	$259.70	$259.70
Purchase #2	$127.79	12.620%	$143.9171	$143.92	$143.90	$143.90
Purchase #3	$211.60	12.821%	$238.7292	$238.73	$238.75	$238.70
Purchase #4	$118.41	10.827%	$131.2303	$131.23	$131.25	$131.20
Purchase #5	$13.86	12.777%	$15.6309	$15.63	$15.65	$15.60
Purchase #6	$200.31	5.457%	$211.2409	$211.24	$211.25	$211.20
Purchase #7	$17.79	13.736%	$20.2336	$20.23	$20.25	$20.20
7 purchase totals =	$918.07		$1,020.6755	$1,020.67	$1,020.75	$1,020.50