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	$138.94	5.554%	$146.6567	$146.66	$146.65	$146.70
Purchase #2	$230.56	11.310%	$256.6363	$256.64	$256.65	$256.60
Purchase #3	$145.94	12.675%	$164.4379	$164.44	$164.45	$164.40
Purchase #4	$9.45	11.388%	$10.5262	$10.53	$10.55	$10.50
Purchase #5	$53.77	13.760%	$61.1688	$61.17	$61.15	$61.20
Purchase #6	$84.70	7.299%	$90.8823	$90.88	$90.90	$90.90
Purchase #7	$62.86	12.535%	$70.7395	$70.74	$70.75	$70.70
7 purchase totals =	$726.22		$801.0477	$801.06	$801.10	$801.00