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	$51.98	5.543%	$54.8613	$54.86	$54.85	$54.90
Purchase #2	$153.80	13.849%	$175.0998	$175.10	$175.10	$175.10
Purchase #3	$104.78	7.140%	$112.2613	$112.26	$112.25	$112.30
Purchase #4	$91.71	3.714%	$95.1161	$95.12	$95.10	$95.10
Purchase #5	$41.25	10.137%	$45.4315	$45.43	$45.45	$45.40
Purchase #6	$19.37	8.836%	$21.0815	$21.08	$21.10	$21.10
Purchase #7	$241.87	10.344%	$266.889	$266.89	$266.90	$266.90
7 purchase totals =	$704.76		$770.7405	$770.74	$770.75	$770.80