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	$29.54	9.870%	$32.4556	$32.46	$32.45	$32.50
Purchase #2	$172.32	13.586%	$195.7314	$195.73	$195.75	$195.70
Purchase #3	$98.73	10.182%	$108.7827	$108.78	$108.80	$108.80
Purchase #4	$61.33	7.819%	$66.1254	$66.13	$66.15	$66.10
Purchase #5	$220.94	3.545%	$228.7723	$228.77	$228.75	$228.80
Purchase #6	$78.94	12.272%	$88.6275	$88.63	$88.65	$88.60
Purchase #7	$112.90	12.573%	$127.0949	$127.09	$127.10	$127.10
7 purchase totals =	$774.70		$847.5898	$847.59	$847.65	$847.60