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	$98.87	12.848%	$111.5728	$111.57	$111.55	$111.60
Purchase #2	$220.45	7.871%	$237.8016	$237.80	$237.80	$237.80
Purchase #3	$34.26	12.302%	$38.4747	$38.47	$38.45	$38.50
Purchase #4	$39.48	9.111%	$43.077	$43.08	$43.10	$43.10
Purchase #5	$38.59	3.520%	$39.9484	$39.95	$39.95	$39.90
Purchase #6	$99.51	9.456%	$108.9197	$108.92	$108.90	$108.90
Purchase #7	$58.59	12.194%	$65.7345	$65.73	$65.75	$65.70
7 purchase totals =	$589.75		$645.5287	$645.52	$645.50	$645.50