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	$125.94	11.499%	$140.4218	$140.42	$140.40	$140.40
Purchase #2	$31.30	8.811%	$34.0578	$34.06	$34.05	$34.10
Purchase #3	$127.78	5.276%	$134.5217	$134.52	$134.50	$134.50
Purchase #4	$50.69	6.735%	$54.104	$54.10	$54.10	$54.10
Purchase #5	$79.59	7.851%	$85.8386	$85.84	$85.85	$85.80
Purchase #6	$30.38	4.255%	$31.6727	$31.67	$31.65	$31.70
Purchase #7	$99.83	9.436%	$109.25	$109.25	$109.25	$109.30
7 purchase totals =	$545.51		$589.8666	$589.86	$589.80	$589.90