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	$29.82	7.183%	$31.962	$31.96	$31.95	$32.00
Purchase #2	$143.39	7.350%	$153.9292	$153.93	$153.95	$153.90
Purchase #3	$86.41	13.218%	$97.8317	$97.83	$97.85	$97.80
Purchase #4	$104.75	6.401%	$111.455	$111.46	$111.45	$111.50
Purchase #5	$144.68	7.312%	$155.259	$155.26	$155.25	$155.30
Purchase #6	$172.67	11.438%	$192.42	$192.42	$192.40	$192.40
Purchase #7	$243.78	8.478%	$264.4477	$264.45	$264.45	$264.40
7 purchase totals =	$925.50		$1,007.3046	$1,007.31	$1,007.30	$1,007.30