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	$50.99	5.695%	$53.8939	$53.89	$53.90	$53.90
Purchase #2	$49.93	4.542%	$52.1978	$52.20	$52.20	$52.20
Purchase #3	$33.78	13.661%	$38.3947	$38.39	$38.40	$38.40
Purchase #4	$93.26	13.333%	$105.6944	$105.69	$105.70	$105.70
Purchase #5	$220.27	3.144%	$227.1953	$227.20	$227.20	$227.20
Purchase #6	$131.39	9.165%	$143.4319	$143.43	$143.45	$143.40
Purchase #7	$226.44	6.685%	$241.5775	$241.58	$241.60	$241.60
7 purchase totals =	$806.06		$862.3855	$862.38	$862.45	$862.40