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	$235.96	5.527%	$249.0015	$249.00	$249.00	$249.00
Purchase #2	$36.28	11.161%	$40.3292	$40.33	$40.35	$40.30
Purchase #3	$42.69	7.694%	$45.9746	$45.97	$45.95	$46.00
Purchase #4	$147.31	9.167%	$160.8139	$160.81	$160.80	$160.80
Purchase #5	$75.78	3.282%	$78.2671	$78.27	$78.25	$78.30
Purchase #6	$44.43	6.630%	$47.3757	$47.38	$47.40	$47.40
Purchase #7	$140.95	7.729%	$151.844	$151.84	$151.85	$151.80
7 purchase totals =	$723.40		$773.6060	$773.60	$773.60	$773.60