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	$51.62	11.226%	$57.4149	$57.41	$57.40	$57.40
Purchase #2	$12.25	8.178%	$13.2518	$13.25	$13.25	$13.30
Purchase #3	$147.57	13.429%	$167.3872	$167.39	$167.40	$167.40
Purchase #4	$237.58	11.120%	$263.9989	$264.00	$264.00	$264.00
Purchase #5	$117.98	11.551%	$131.6079	$131.61	$131.60	$131.60
Purchase #6	$153.90	4.114%	$160.2314	$160.23	$160.25	$160.20
Purchase #7	$62.63	13.666%	$71.189	$71.19	$71.20	$71.20
7 purchase totals =	$783.53		$865.0811	$865.08	$865.10	$865.10