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	$39.61	10.640%	$43.8245	$43.82	$43.80	$43.80
Purchase #2	$248.30	10.140%	$273.4776	$273.48	$273.50	$273.50
Purchase #3	$104.25	5.186%	$109.6564	$109.66	$109.65	$109.70
Purchase #4	$148.83	6.601%	$158.6543	$158.65	$158.65	$158.70
Purchase #5	$85.75	11.622%	$95.7159	$95.72	$95.70	$95.70
Purchase #6	$151.74	4.392%	$158.4044	$158.40	$158.40	$158.40
Purchase #7	$148.35	3.424%	$153.4295	$153.43	$153.45	$153.40
7 purchase totals =	$926.83		$993.1626	$993.16	$993.15	$993.20