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	$122.43	12.788%	$138.0863	$138.09	$138.10	$138.10
Purchase #2	$95.45	4.554%	$99.7968	$99.80	$99.80	$99.80
Purchase #3	$112.48	13.194%	$127.3206	$127.32	$127.30	$127.30
Purchase #4	$203.48	10.383%	$224.6073	$224.61	$224.60	$224.60
Purchase #5	$80.25	12.272%	$90.0983	$90.10	$90.10	$90.10
Purchase #6	$33.92	5.474%	$35.7768	$35.78	$35.80	$35.80
Purchase #7	$9.58	12.364%	$10.7645	$10.76	$10.75	$10.80
7 purchase totals =	$657.59		$726.4506	$726.46	$726.45	$726.50