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	$88.41	12.271%	$99.2588	$99.26	$99.25	$99.30
Purchase #2	$52.76	9.188%	$57.6076	$57.61	$57.60	$57.60
Purchase #3	$69.85	3.801%	$72.505	$72.51	$72.50	$72.50
Purchase #4	$149.60	5.126%	$157.2685	$157.27	$157.25	$157.30
Purchase #5	$170.26	13.687%	$193.5635	$193.56	$193.55	$193.60
Purchase #6	$151.38	13.579%	$171.9359	$171.94	$171.95	$171.90
Purchase #7	$34.92	13.245%	$39.5452	$39.55	$39.55	$39.50
7 purchase totals =	$717.18		$791.6845	$791.70	$791.65	$791.70