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	$7.43	6.526%	$7.9149	$7.91	$7.90	$7.90
Purchase #2	$126.92	3.579%	$131.4625	$131.46	$131.45	$131.50
Purchase #3	$64.39	9.792%	$70.6951	$70.70	$70.70	$70.70
Purchase #4	$187.32	11.106%	$208.1238	$208.12	$208.10	$208.10
Purchase #5	$26.56	9.393%	$29.0548	$29.05	$29.05	$29.10
Purchase #6	$19.64	10.787%	$21.7586	$21.76	$21.75	$21.80
Purchase #7	$132.96	8.587%	$144.3773	$144.38	$144.40	$144.40
7 purchase totals =	$565.22		$613.3870	$613.38	$613.35	$613.50