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	$81.71	6.237%	$86.8063	$86.81	$86.80	$86.80
Purchase #2	$171.99	7.845%	$185.4826	$185.48	$185.50	$185.50
Purchase #3	$43.29	11.788%	$48.393	$48.39	$48.40	$48.40
Purchase #4	$98.46	6.649%	$105.0066	$105.01	$105.00	$105.00
Purchase #5	$186.92	3.200%	$192.9014	$192.90	$192.90	$192.90
Purchase #6	$147.66	4.583%	$154.4273	$154.43	$154.45	$154.40
Purchase #7	$115.43	10.334%	$127.3585	$127.36	$127.35	$127.40
7 purchase totals =	$845.46		$900.3757	$900.38	$900.40	$900.40