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	$112.68	13.746%	$128.169	$128.17	$128.15	$128.20
Purchase #2	$123.47	12.657%	$139.0976	$139.10	$139.10	$139.10
Purchase #3	$86.50	13.588%	$98.2536	$98.25	$98.25	$98.30
Purchase #4	$234.31	4.836%	$245.6412	$245.64	$245.65	$245.60
Purchase #5	$7.52	8.758%	$8.1786	$8.18	$8.20	$8.20
Purchase #6	$57.71	3.676%	$59.8314	$59.83	$59.85	$59.80
Purchase #7	$9.31	13.431%	$10.5604	$10.56	$10.55	$10.60
7 purchase totals =	$631.50		$689.7318	$689.73	$689.75	$689.80