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	$20.98	3.789%	$21.7749	$21.77	$21.75	$21.80
Purchase #2	$242.28	4.308%	$252.7174	$252.72	$252.70	$252.70
Purchase #3	$84.30	6.222%	$89.5451	$89.55	$89.55	$89.50
Purchase #4	$108.90	7.420%	$116.9804	$116.98	$117.00	$117.00
Purchase #5	$72.42	13.555%	$82.2365	$82.24	$82.25	$82.20
Purchase #6	$236.73	7.836%	$255.2802	$255.28	$255.30	$255.30
Purchase #7	$184.46	7.235%	$197.8057	$197.81	$197.80	$197.80
7 purchase totals =	$950.07		$1,016.3402	$1,016.35	$1,016.35	$1,016.30