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	$65.45	7.421%	$70.307	$70.31	$70.30	$70.30
Purchase #2	$204.31	13.865%	$232.6376	$232.64	$232.65	$232.60
Purchase #3	$18.43	13.507%	$20.9193	$20.92	$20.90	$20.90
Purchase #4	$107.94	6.826%	$115.308	$115.31	$115.30	$115.30
Purchase #5	$101.35	9.850%	$111.333	$111.33	$111.35	$111.30
Purchase #6	$46.29	13.468%	$52.5243	$52.52	$52.50	$52.50
Purchase #7	$239.42	11.732%	$267.5088	$267.51	$267.50	$267.50
7 purchase totals =	$783.19		$870.5380	$870.54	$870.50	$870.40