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	$117.63	8.595%	$127.7403	$127.74	$127.75	$127.70
Purchase #2	$82.42	6.277%	$87.5935	$87.59	$87.60	$87.60
Purchase #3	$171.55	4.246%	$178.834	$178.83	$178.85	$178.80
Purchase #4	$52.91	13.227%	$59.9084	$59.91	$59.90	$59.90
Purchase #5	$82.62	11.134%	$91.8189	$91.82	$91.80	$91.80
Purchase #6	$122.33	10.713%	$135.4352	$135.44	$135.45	$135.40
Purchase #7	$164.44	8.578%	$178.5457	$178.55	$178.55	$178.50
7 purchase totals =	$793.90		$859.8760	$859.88	$859.90	$859.70