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	$170.59	10.827%	$189.0598	$189.06	$189.05	$189.10
Purchase #2	$184.42	12.677%	$207.7989	$207.80	$207.80	$207.80
Purchase #3	$58.97	11.714%	$65.8777	$65.88	$65.90	$65.90
Purchase #4	$69.63	5.763%	$73.6428	$73.64	$73.65	$73.60
Purchase #5	$100.85	8.732%	$109.6562	$109.66	$109.65	$109.70
Purchase #6	$73.89	6.756%	$78.882	$78.88	$78.90	$78.90
Purchase #7	$127.30	13.486%	$144.4677	$144.47	$144.45	$144.50
7 purchase totals =	$785.65		$869.3851	$869.39	$869.40	$869.50