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	$27.92	4.623%	$29.2107	$29.21	$29.20	$29.20
Purchase #2	$90.53	6.621%	$96.524	$96.52	$96.50	$96.50
Purchase #3	$128.43	9.429%	$140.5397	$140.54	$140.55	$140.50
Purchase #4	$40.68	4.709%	$42.5956	$42.60	$42.60	$42.60
Purchase #5	$24.77	4.531%	$25.8923	$25.89	$25.90	$25.90
Purchase #6	$127.86	13.823%	$145.5341	$145.53	$145.55	$145.50
Purchase #7	$177.89	5.633%	$187.9105	$187.91	$187.90	$187.90
7 purchase totals =	$618.08		$668.2069	$668.20	$668.20	$668.10