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	$178.59	7.211%	$191.4681	$191.47	$191.45	$191.50
Purchase #2	$213.28	3.105%	$219.9023	$219.90	$219.90	$219.90
Purchase #3	$100.90	12.466%	$113.4782	$113.48	$113.50	$113.50
Purchase #4	$113.79	6.818%	$121.5482	$121.55	$121.55	$121.50
Purchase #5	$116.50	7.366%	$125.0814	$125.08	$125.10	$125.10
Purchase #6	$247.48	9.205%	$270.2605	$270.26	$270.25	$270.30
Purchase #7	$160.48	7.270%	$172.1469	$172.15	$172.15	$172.10
7 purchase totals =	$1,131.02		$1,213.8856	$1,213.89	$1,213.90	$1,213.90