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	$72.86	10.707%	$80.6611	$80.66	$80.65	$80.70
Purchase #2	$245.32	5.346%	$258.4348	$258.43	$258.45	$258.40
Purchase #3	$79.28	4.787%	$83.0751	$83.08	$83.10	$83.10
Purchase #4	$73.85	12.310%	$82.9409	$82.94	$82.95	$82.90
Purchase #5	$51.70	9.445%	$56.5831	$56.58	$56.60	$56.60
Purchase #6	$152.77	12.525%	$171.9044	$171.90	$171.90	$171.90
Purchase #7	$154.66	12.432%	$173.8873	$173.89	$173.90	$173.90
7 purchase totals =	$830.44		$907.4867	$907.48	$907.55	$907.50