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	$137.74	12.762%	$155.3184	$155.32	$155.30	$155.30
Purchase #2	$118.88	9.833%	$130.5695	$130.57	$130.55	$130.60
Purchase #3	$84.72	6.114%	$89.8998	$89.90	$89.90	$89.90
Purchase #4	$79.28	9.211%	$86.5825	$86.58	$86.60	$86.60
Purchase #5	$29.86	13.109%	$33.7743	$33.77	$33.75	$33.80
Purchase #6	$147.81	13.504%	$167.7703	$167.77	$167.75	$167.80
Purchase #7	$158.78	3.258%	$163.9531	$163.95	$163.95	$164.00
7 purchase totals =	$757.07		$827.8679	$827.86	$827.80	$828.00