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	$87.72	13.377%	$99.4543	$99.45	$99.45	$99.50
Purchase #2	$174.30	5.316%	$183.5658	$183.57	$183.55	$183.60
Purchase #3	$102.82	8.303%	$111.3571	$111.36	$111.35	$111.40
Purchase #4	$216.29	11.431%	$241.0141	$241.01	$241.00	$241.00
Purchase #5	$30.46	7.212%	$32.6568	$32.66	$32.65	$32.70
Purchase #6	$209.72	4.555%	$219.2727	$219.27	$219.25	$219.30
Purchase #7	$38.61	11.332%	$42.9853	$42.99	$43.00	$43.00
7 purchase totals =	$859.92		$930.3061	$930.31	$930.25	$930.50