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	$74.78	4.833%	$78.3941	$78.39	$78.40	$78.40
Purchase #2	$90.96	9.826%	$99.8977	$99.90	$99.90	$99.90
Purchase #3	$191.72	8.249%	$207.535	$207.54	$207.55	$207.50
Purchase #4	$13.61	13.655%	$15.4684	$15.47	$15.45	$15.50
Purchase #5	$163.96	7.307%	$175.9406	$175.94	$175.95	$175.90
Purchase #6	$232.65	9.628%	$255.0495	$255.05	$255.05	$255.00
Purchase #7	$90.55	9.331%	$98.9992	$99.00	$99.00	$99.00
7 purchase totals =	$858.23		$931.2845	$931.29	$931.30	$931.20