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	$33.51	12.123%	$37.5724	$37.57	$37.55	$37.60
Purchase #2	$233.46	13.722%	$265.4954	$265.50	$265.50	$265.50
Purchase #3	$108.95	3.442%	$112.7001	$112.70	$112.70	$112.70
Purchase #4	$34.88	7.261%	$37.4126	$37.41	$37.40	$37.40
Purchase #5	$170.66	5.388%	$179.8552	$179.86	$179.85	$179.90
Purchase #6	$236.41	8.768%	$257.1384	$257.14	$257.15	$257.10
Purchase #7	$117.66	4.788%	$123.2936	$123.29	$123.30	$123.30
7 purchase totals =	$935.53		$1,013.4677	$1,013.47	$1,013.45	$1,013.50