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	$92.49	7.144%	$99.0975	$99.10	$99.10	$99.10
Purchase #2	$118.35	11.844%	$132.3674	$132.37	$132.35	$132.40
Purchase #3	$212.69	13.693%	$241.8136	$241.81	$241.80	$241.80
Purchase #4	$33.47	10.581%	$37.0115	$37.01	$37.00	$37.00
Purchase #5	$160.51	5.531%	$169.3878	$169.39	$169.40	$169.40
Purchase #6	$111.67	4.134%	$116.2864	$116.29	$116.30	$116.30
Purchase #7	$107.93	11.142%	$119.9556	$119.96	$119.95	$120.00
7 purchase totals =	$837.11		$915.9198	$915.93	$915.90	$916.00