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	$88.60	12.184%	$99.395	$99.40	$99.40	$99.40
Purchase #2	$38.44	7.784%	$41.4322	$41.43	$41.45	$41.40
Purchase #3	$142.74	5.179%	$150.1325	$150.13	$150.15	$150.10
Purchase #4	$210.84	12.328%	$236.8324	$236.83	$236.85	$236.80
Purchase #5	$140.51	10.481%	$155.2369	$155.24	$155.25	$155.20
Purchase #6	$158.63	12.833%	$178.987	$178.99	$179.00	$179.00
Purchase #7	$48.38	10.221%	$53.3249	$53.32	$53.30	$53.30
7 purchase totals =	$828.14		$915.3409	$915.34	$915.40	$915.20