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	$37.25	8.611%	$40.4576	$40.46	$40.45	$40.50
Purchase #2	$98.83	11.232%	$109.9306	$109.93	$109.95	$109.90
Purchase #3	$128.69	12.663%	$144.986	$144.99	$145.00	$145.00
Purchase #4	$81.91	3.109%	$84.4566	$84.46	$84.45	$84.50
Purchase #5	$71.82	9.720%	$78.8009	$78.80	$78.80	$78.80
Purchase #6	$161.28	13.213%	$182.5899	$182.59	$182.60	$182.60
Purchase #7	$67.87	5.466%	$71.5798	$71.58	$71.60	$71.60
7 purchase totals =	$647.65		$712.8014	$712.81	$712.85	$712.90