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	$9.38	3.740%	$9.7308	$9.73	$9.75	$9.70
Purchase #2	$85.59	3.838%	$88.8749	$88.87	$88.85	$88.90
Purchase #3	$134.75	12.640%	$151.7824	$151.78	$151.80	$151.80
Purchase #4	$11.82	10.732%	$13.0885	$13.09	$13.10	$13.10
Purchase #5	$204.44	13.203%	$231.4322	$231.43	$231.45	$231.40
Purchase #6	$109.52	12.726%	$123.4575	$123.46	$123.45	$123.50
Purchase #7	$37.37	8.149%	$40.4153	$40.42	$40.40	$40.40
7 purchase totals =	$592.87		$658.7816	$658.78	$658.80	$658.80