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	$85.37	6.278%	$90.7295	$90.73	$90.75	$90.70
Purchase #2	$173.93	5.147%	$182.8822	$182.88	$182.90	$182.90
Purchase #3	$61.25	9.592%	$67.1251	$67.13	$67.15	$67.10
Purchase #4	$53.73	5.223%	$56.5363	$56.54	$56.55	$56.50
Purchase #5	$108.39	7.727%	$116.7653	$116.77	$116.75	$116.80
Purchase #6	$205.53	12.787%	$231.8111	$231.81	$231.80	$231.80
Purchase #7	$149.86	8.157%	$162.0841	$162.08	$162.10	$162.10
7 purchase totals =	$838.06		$907.9336	$907.94	$908.00	$907.90