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	$78.39	9.150%	$85.5627	$85.56	$85.55	$85.60
Purchase #2	$217.64	10.859%	$241.2735	$241.27	$241.25	$241.30
Purchase #3	$80.36	3.679%	$83.3164	$83.32	$83.30	$83.30
Purchase #4	$142.46	10.613%	$157.5793	$157.58	$157.60	$157.60
Purchase #5	$170.48	5.670%	$180.1462	$180.15	$180.15	$180.10
Purchase #6	$132.69	8.313%	$143.7205	$143.72	$143.70	$143.70
Purchase #7	$108.26	11.484%	$120.6926	$120.69	$120.70	$120.70
7 purchase totals =	$930.28		$1,012.2912	$1,012.29	$1,012.25	$1,012.30