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	$170.93	7.394%	$183.5686	$183.57	$183.55	$183.60
Purchase #2	$130.65	10.487%	$144.3513	$144.35	$144.35	$144.40
Purchase #3	$98.80	4.542%	$103.2875	$103.29	$103.30	$103.30
Purchase #4	$59.46	10.856%	$65.915	$65.92	$65.90	$65.90
Purchase #5	$39.55	12.572%	$44.5222	$44.52	$44.50	$44.50
Purchase #6	$21.46	6.281%	$22.8079	$22.81	$22.80	$22.80
Purchase #7	$52.39	10.425%	$57.8517	$57.85	$57.85	$57.90
7 purchase totals =	$573.24		$622.3042	$622.31	$622.25	$622.40