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	$35.50	13.315%	$40.2268	$40.23	$40.25	$40.20
Purchase #2	$49.63	9.351%	$54.2709	$54.27	$54.25	$54.30
Purchase #3	$10.34	10.664%	$11.4427	$11.44	$11.45	$11.40
Purchase #4	$208.84	11.627%	$233.1218	$233.12	$233.10	$233.10
Purchase #5	$200.27	8.123%	$216.5379	$216.54	$216.55	$216.50
Purchase #6	$239.86	6.825%	$256.2304	$256.23	$256.25	$256.20
Purchase #7	$136.37	12.528%	$153.4544	$153.45	$153.45	$153.50
7 purchase totals =	$880.81		$965.2849	$965.28	$965.30	$965.20