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	$36.82	8.720%	$40.0307	$40.03	$40.05	$40.00
Purchase #2	$52.59	9.259%	$57.4593	$57.46	$57.45	$57.50
Purchase #3	$206.74	12.837%	$233.2792	$233.28	$233.30	$233.30
Purchase #4	$234.99	8.824%	$255.7255	$255.73	$255.75	$255.70
Purchase #5	$205.59	3.267%	$212.3066	$212.31	$212.30	$212.30
Purchase #6	$38.95	4.116%	$40.5532	$40.55	$40.55	$40.60
Purchase #7	$211.44	10.262%	$233.138	$233.14	$233.15	$233.10
7 purchase totals =	$987.12		$1,072.4925	$1,072.50	$1,072.55	$1,072.50