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	$81.54	10.431%	$90.0454	$90.05	$90.05	$90.00
Purchase #2	$78.37	11.730%	$87.5628	$87.56	$87.55	$87.60
Purchase #3	$45.53	10.383%	$50.2574	$50.26	$50.25	$50.30
Purchase #4	$131.51	9.706%	$144.2744	$144.27	$144.25	$144.30
Purchase #5	$135.38	4.158%	$141.0091	$141.01	$141.00	$141.00
Purchase #6	$42.29	4.711%	$44.2823	$44.28	$44.30	$44.30
Purchase #7	$12.55	13.298%	$14.2189	$14.22	$14.20	$14.20
7 purchase totals =	$527.17		$571.6503	$571.65	$571.60	$571.70