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	$136.51	4.195%	$142.2366	$142.24	$142.25	$142.20
Purchase #2	$31.77	5.244%	$33.436	$33.44	$33.45	$33.40
Purchase #3	$93.58	9.563%	$102.5291	$102.53	$102.55	$102.50
Purchase #4	$95.47	10.267%	$105.2719	$105.27	$105.25	$105.30
Purchase #5	$137.92	4.241%	$143.7692	$143.77	$143.75	$143.80
Purchase #6	$75.40	6.496%	$80.298	$80.30	$80.30	$80.30
Purchase #7	$158.62	13.570%	$180.1447	$180.14	$180.15	$180.10
7 purchase totals =	$729.27		$787.6855	$787.69	$787.70	$787.60