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	$126.74	8.751%	$137.831	$137.83	$137.85	$137.80
Purchase #2	$76.60	7.747%	$82.5342	$82.53	$82.55	$82.50
Purchase #3	$209.81	6.753%	$223.9785	$223.98	$224.00	$224.00
Purchase #4	$33.82	13.569%	$38.409	$38.41	$38.40	$38.40
Purchase #5	$144.67	8.169%	$156.4881	$156.49	$156.50	$156.50
Purchase #6	$157.59	8.743%	$171.3681	$171.37	$171.35	$171.40
Purchase #7	$24.97	10.192%	$27.5149	$27.51	$27.50	$27.50
7 purchase totals =	$774.20		$838.1238	$838.12	$838.15	$838.10