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	$51.57	11.777%	$57.6434	$57.64	$57.65	$57.60
Purchase #2	$95.65	9.251%	$104.4986	$104.50	$104.50	$104.50
Purchase #3	$22.56	11.845%	$25.2322	$25.23	$25.25	$25.20
Purchase #4	$170.60	9.709%	$187.1636	$187.16	$187.15	$187.20
Purchase #5	$48.65	5.133%	$51.1472	$51.15	$51.15	$51.10
Purchase #6	$85.94	4.374%	$89.699	$89.70	$89.70	$89.70
Purchase #7	$89.71	12.838%	$101.227	$101.23	$101.25	$101.20
7 purchase totals =	$564.68		$616.6110	$616.61	$616.65	$616.50