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	$49.76	5.241%	$52.3679	$52.37	$52.35	$52.40
Purchase #2	$133.69	7.276%	$143.4173	$143.42	$143.40	$143.40
Purchase #3	$33.55	5.755%	$35.4808	$35.48	$35.50	$35.50
Purchase #4	$218.40	11.481%	$243.4745	$243.47	$243.45	$243.50
Purchase #5	$53.25	6.249%	$56.5776	$56.58	$56.60	$56.60
Purchase #6	$226.56	10.487%	$250.3193	$250.32	$250.30	$250.30
Purchase #7	$201.86	8.113%	$218.2369	$218.24	$218.25	$218.20
7 purchase totals =	$917.07		$999.8743	$999.88	$999.85	$999.90