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	$138.52	3.873%	$143.8849	$143.88	$143.90	$143.90
Purchase #2	$134.54	9.680%	$147.5635	$147.56	$147.55	$147.60
Purchase #3	$46.81	6.824%	$50.0043	$50.00	$50.00	$50.00
Purchase #4	$248.96	3.672%	$258.1018	$258.10	$258.10	$258.10
Purchase #5	$121.31	4.747%	$127.0686	$127.07	$127.05	$127.10
Purchase #6	$57.67	3.786%	$59.8534	$59.85	$59.85	$59.90
Purchase #7	$18.87	7.804%	$20.3426	$20.34	$20.35	$20.30
7 purchase totals =	$766.68		$806.8191	$806.80	$806.80	$806.90